Race — Condition Hackviser

Implement locks (Mutexes) to ensure that only one thread can access a resource at a time.

The binary checks if the user owns the file before reading it. However, if we can swap the file after the check but before the read, we can trick the program.

HVthreads_are_not_atomic_2e6a9f

fclose(fp);

Flag format: HV... or flag...

user@hackviser:~$ ls -la /opt/vuln_binary -rwsr-sr-x 1 root root 16784 Jan 1 12:00 /opt/vuln_binary

Run your attack script. A successful exploit will result in the unexpected outcome. For example, if it's a coupon lab, you might see your account credited 20 times from a single coupon. If it's a banking lab, you might drain an account into the negative. The lab environment will clearly indicate when you've won the race by updating your score or presenting a flag. race condition hackviser

We need two parallel processes:

Classified as CWE-362 in the Common Weakness Enumeration, race conditions occur when program behavior depends on the uncontrolled relative timing of concurrent events. Web applications rely heavily on threads to handle multiple users concurrently, and when multiple HTTP requests arrive at a web server, each request is typically assigned to a separate thread. When these requests interact with shared data—such as during database updates or token generation—race conditions can easily occur, especially when changes made by one request aren't properly synchronized with other requests. Implement locks (Mutexes) to ensure that only one