If you’re involved in video streaming or media processing, chances are you’ve encountered Bento4, an open-source toolkit widely used for working with MP4 files. But in 2022, a severe security flaw was uncovered: CVE-2022-3662. This post breaks down what happened, why it matters, and how an attacker could exploit it—with code snippets and links to more info.

What is Bento4 and What’s mp42hls?

Bento4: A C++-based library suite for reading, writing, and processing MP4 files. Often embedded in video streaming solutions.

mp42hls: One of Bento4’s tools—it converts MP4 files into HLS (HTTP Live Streaming) format.

Where: Inside the GetOffset method in Ap4Sample.h

- Effect: Under certain circumstances, memory is freed but still used (classic *use-after-free*), allowing an attacker to hijack the app’s behavior.
- How: Simply by sending a specially crafted MP4 file (remotely), an attacker could trigger the bug.

Identifiers:

- Vulnerability: CVE-2022-3662, VDB-212002 (VulDB)
- Bento4 Issue: GitHub page

Where’s the Bug?

The problematic function is in the Bento4 source code file: Source/Core/Ap4Sample.h.

Here’s a simplified (and relevant) code snippet

// Ap4Sample.h, simplified example for explanation
class AP4_Sample {
public:
    // ...
    AP4_Offset GetOffset() const {
        if (m_MemoryBlock == NULL) {
            return ;
        }
        return m_Offset;
    }

private:
    AP4_MemoryBlock* m_MemoryBlock; // gets freed elsewhere!
    AP4_Offset m_Offset;
};

m_MemoryBlock is a pointer to some memory.

- If the pointer is free’d but not set to NULL, and code calls GetOffset(), the function could access invalid (dangling) memory.

Craft a malicious MP4 file that manipulates Bento4’s sample table.

2. The file triggers a code path where m_MemoryBlock is freed due to an error, but GetOffset() is still called.

The function accesses freed memory.

4. Result: Attacker might run code of their choice on the system running mp42hls—especially dangerous if served automatically (e.g., in a cloud media pipeline).

Example (simplified)

Assume we can create an MP4 file which causes Bento4 to free a memory block but not update pointers correctly:

// Example dangerous flow
AP4_Sample* sample = new AP4_Sample();
free(sample->m_MemoryBlock);        // Frees memory
// ... app logic ...
sample->GetOffset();                // Uses freed memory!

If GetOffset() tries to dereference this pointer, the attacker could supply controlled data—maybe even wind up controlling program instruction flow.

Proof of Concept (PoC)

Public exploits have been crafted, according to VulDB and GitHub security advisories. Here’s a very simple outline based on the real exploits:

# An attacker makes a special MP4 file (evil.mp4)
./mp42hls evil.mp4 output_dir

- Running this command (for example on a web server or video pipeline) with a malicious file can crash the process or lead to arbitrary code execution.

If you use Bento4 or tools built with it (like mp42hls)

- Update immediately—the bug is fixed in the latest versions. Bento4 Releases

References & Further Reading

- NIST NVD CVE-2022-3662 page
- VulDB Entry: VDB-212002
- Bento4 GitHub
- mp42hls tool
- Original Bug Report on GitHub (if public)

Update your software ASAP.

Stay secure, and watch what you feed into your media tools!

Timeline

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