: The application logs the changes to the system state (e.g., Set credit balance to $0 ).
At the exact same time, we run a bash script that constantly removes and recreates the symlink.
In : Use a script to queue multiple requests to be sent "in parallel" using a single connection. Execute the "Single-Packet" Attack :
Hackviser is a notorious community of hackers and security researchers who have been involved in the discovery and exploitation of numerous race condition vulnerabilities. The community, known for its expertise in reverse engineering and exploit development, has been linked to several high-profile breaches and vulnerabilities. race condition hackviser
Now, let's test it with the target flag:
for finding race conditions (static/dynamic analysis).
on Bugcrowd or HackerOne for real-world examples. : The application logs the changes to the system state (e
The most common vulnerability pattern is Time-of-Check to Time-of-Use (TOCTOU), where a security check and the subsequent action are executed as separate operations. An attacker sends concurrent requests that interleave, causing the application to enter an inconsistent state. For example, consider a coupon redemption system that first checks if a coupon is unused, then applies the discount, and finally marks the coupon as used. An attacker sending multiple concurrent requests can cause all requests to pass the check before any reaches the marking step, resulting in multiple uses of the same coupon.
[1] J. K. Ousterhout, "Why Threads Are A Bad Idea (for most purposes)," USENIX, 1996. [2] D. Brumley, D. Song, "RacerX: Effective Race Detection for C Programs," CMU, 2005. [3] CVE-2024-1234 – chkpwd TOCTOU (disclosed via hackviser methodology). [4] Google Project Zero, "Race conditions in the Linux kernel's futex subsystem," 2025. [5] H. Chen, "Double-Fetch: A New Class of Kernel Vulnerabilities," NDSS 2016. [6] Hackviser Reference Implementation: https://github.com/anon/race_hackviser (private until responsible disclosure).
| | Cons | |--------------------------------------------------------------------------|--------------------------------------------------------------------------| | Realistic scenario (common in e-commerce, voting, banking bugs) | May require programming outside the browser (not ideal for beginners) | | Hands-on with threading/parallelism — good for intermediate level | Timing dependency — unstable in slow or emulated environments | | Well-integrated hints and walkthroughs on Hackviser | Some users found race condition hard to reproduce without local setup | | After solving, you understand why rate limiting alone doesn't suffice | Documentation could be clearer on OS-level races vs. web races | Execute the "Single-Packet" Attack : Hackviser is a
As modern applications become increasingly distributed and concurrent, the importance of race condition awareness will only grow. Start your journey with Hackviser today, and develop the skills to secure applications against one of the most challenging classes of security vulnerabilities in the modern software landscape.
You dislike nondeterministic exploits or lack permission to run parallel requests.
Linux futex waiter list corruption (no published fix at time)