Modern defenses against race conditions include:
| Mitigation | Bypass via Hackviser |
|------------|----------------------|
| File locking (fcntl) | Use /proc/self/fd symlink attack to bypass lock scope |
| Atomic operations (CAS) | Race after CAS but before commit (e.g., double-fetch) |
| Transaction isolation (SERIALIZABLE) | Use read-only race + out-of-band channel (cache side-channel) |
| Deterministic scheduling (TSO) | Introduce async signals or page faults to deschedule victim |
The hackviser maintains a mitigation bypass matrix updated from CVE data.
Create a dummy file that we own to pass the permission check.
user@hackviser:~$ touch /tmp/dummy
user@hackviser:~$ ln -s /tmp/dummy /tmp/link
You’re given a vulnerable endpoint or binary where a shared resource (file, counter, balance, or token) is accessed without proper locking mechanisms. The goal is to send multiple concurrent requests/processes to manipulate the state in an unintended way—e.g., bypassing a restriction, applying a coupon multiple times, or exceeding a limit. race condition hackviser
Example scenario from Hackviser:
“A payment system checks balance before deducting. Two threads pass the ‘sufficient funds’ check before either deducts, allowing a negative balance.”
A traditional hacker looks for logic flaws. A Race Condition Hackviser, however, looks for timing flaws. The term "hackviser" implies a visual or diagnostic layer that helps the attacker see the slices of time where the system is vulnerable.
In practice, a Race Condition Hackviser is a workflow that combines: Create a dummy file that we own to pass the permission check
The "adviser" part comes from the interpretation of data. It tells you: "Here is the 15ms window where the database hasn't committed the first transaction before the second transaction reads the balance."
Race conditions occur when the outcome of a process depends on the non-deterministic order of execution between concurrent threads or processes. While classic examples (e.g., mkdir/symlink TOCTOU) have been known since the 1990s, modern systems have reintroduced them through:
First, we identify the SUID binary on the system.
user@hackviser:~$ find / -perm -4000 -type f 2>/dev/null
/usr/bin/passwd
...
/opt/vuln_binary
We check the permissions and ownership:
user@hackviser:~$ ls -la /opt/vuln_binary
-rwsr-sr-x 1 root root 16784 Jan 1 12:00 /opt/vuln_binary
The s in the permissions indicates it runs with root privileges.
We run the binary to understand its logic:
user@hackviser:~$ /opt/vuln_binary
Usage: ./vuln_binary <file_to_read>
Let's test it with a file we own:
user@hackviser:~$ echo "hello" > /tmp/myfile.txt
user@hackviser:~$ /opt/vuln_binary /tmp/myfile.txt
Access Granted.
Reading file...
hello
Now, let's test it with the target flag: You’re given a vulnerable endpoint or binary where
user@hackviser:~$ /opt/vuln_binary /root/flag.txt
Access Denied. You do not own this file.
Hypothesis: 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.