A new vulnerability, CVE-2022-3663, was discovered in the widely used multimedia tool, Axiomatic Bento4. This long-read article will break down what this bug is, how it can be exploited, and what it means for users and developers. We’ll use simple language and show you concrete details, including real code snippets and links to official resources.

What is Bento4?

Bento4 is an open-source C++ library for reading, writing, and processing MP4 files. Many video editing and processing tools use Bento4 under the hood.

A Closer Look at the Vulnerability

- Identifier: CVE-2022-3663
- Bento4 Version: Affected up to at least commit f8d1aaa

Severity: Problematic

- Exploit: Publicly disclosed (VDB-212003)

Why Does It Matter?

A null pointer dereference happens when a program tries to use a pointer that hasn’t been properly set. In practice, this can make the whole application crash. While it usually isn’t enough for an attacker to take over your computer directly, it can be used to trigger denial of service (DoS) remotely — making affected video processing servers or apps shut down.

The Core Problem: Failing to Check for Null

The vulnerable function, AP4_StsdAtom, doesn’t handle some invalid data correctly. With a malicious MP4 file, it’s possible for certain pointers not to be properly initialized before use.

Here’s an example code snippet from the vulnerable source code (Ap4StsdAtom.cpp)

// Ap4StsdAtom.cpp (simplified)
AP4_StsdAtom::AP4_StsdAtom(AP4_ByteStream& stream, AP4_Size size, ...)
{
    // ...
    m_Entries = new AP4_Array<AP4_SampleEntry*>();
    unsigned int entry_count;
    stream.ReadUI32(entry_count); // attacker controls entry_count!

    for (unsigned int i=; i<entry_count; i++) {
        AP4_SampleEntry* entry = AP4_SampleEntry::Create(stream, ...);
        // Bad: doesn't check if entry is NULL!
        m_Entries->Append(entry); // Potential null pointer dereference
    }
    // ...
}

What’s wrong here?
The code reads entry_count from the MP4 file, then loops that many times, blindly accepting whatever comes from the file — even if the function failed and returned NULL. This can crash the software.

Proof-of-Concept Exploit

Researchers have publicly released a sample exploit that triggers the crash, which usually involves passing a corrupted MP4 file to a Bento4-powered application, e.g.:

mp4fragment malicious.mp4 output.mp4

Result: The application crashes with a segmentation fault.

Sample Malicious MP4:
GitHub and VulDB maintainers have confirmed the existence of proof-of-concept files (you can see the original PoC).

Original References and More Reading

- Official CVE Entry (NVD)
- VulDB Advisory (VDB-212003)
- Bento4 GitHub
- Original Patch Discussion (if available)

Who’s at Risk?

You are at risk if you run tools or services using Bento4’s MP4fragment functionality, and you process MP4 files from untrusted sources (including the open internet or user uploads).

How to Mitigate

1. Update Bento4: Check for new releases or security patches. Upgrading to the latest version reduces risk.

Filter Input Files: Reject or scan any MP4 files received from unknown or untrusted sources.

3. Crash Monitoring: Set up monitoring to detect if your services are crashing unexpectedly (could signal targeted attacks).

Patch Yourself: If you’re a developer, add null checks before appending sample entries

// Safe Patch
if (entry) {
    m_Entries->Append(entry);
} else {
    // Handle failure, skip or abort
}

Conclusion

While CVE-2022-3663 isn’t likely to lead to remote code execution, it does allow attackers to crash your services remotely — which is never good for reliability or trust. Always keep your third-party libraries updated, check for advisories, and handle files from stranger’s emails with care!

Got more questions or need help patching? Check the references above, or dive into the Bento4 GitHub repo.

Timeline

Published on: 10/26/2022 19:15:00 UTC
Last modified on: 10/28/2022 17:29:00 UTC