The open-source software project FFmpeg is an incredibly powerful toolset for multimedia handling, allowing for the encoding, decoding, and transcoding of video and audio streams. In this post, we will be examining a recently discovered vulnerability (CVE-2024-36617) in the Core Audio Format (CAF) decoder of FFmpeg version n6.1.1. This vulnerability presents an integer overflow issue, which poses security risks and has the potential to be exploited by malicious parties.
In short, when FFmpeg processes a CAF file, an integer overflow can occur in the CAF decoder, resulting in possible crashes and code execution. We will answer critical questions surrounding the vulnerability, outline reproducible steps to demonstrate the exploit, and provide links to critical resources such as patches and original references.
Vulnerability Breakdown
In FFmpeg n6.1.1, the CAF decoder reads the packet table headers where a 32-bit integer value is read and multiplied by another integer. This multiplication has the potential to produce an overflow, resulting in incorrect values. Subsequently, these values can trigger memory allocation issues or crashes.
Here's a code snippet from FFmpeg's CAF decoder (libavformat/cafdec.c) that demonstrates the problematic calculation (lines 277-280):
/* Read packet table entries */
for (i = ; i < total_packets; i++) {
entries[i].timestamp = avio_rl64(pb) * (st->time_base.den) / st->time_base.num;
}
In this snippet, the programmer reads a 32-bit value (avio_rl64(pb)) and multiplies it with the time_base values. If both values are large enough, this multiplication could result in an integer overflow.
Exploit Details
Due to the nature of the integer overflow vulnerability, an attacker could craft a malicious CAF file that triggers the issue. Subsequently, this crafted file can cause the FFmpeg process to either crash or allow code execution depending on how the overflowed value impacts the subsequent memory allocation.
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Upon running this command, the FFmpeg process might generate a crash or result in undefined behavior due to the exploit.
Patching and Mitigation
The FFmpeg project has already merged a patch fixing this vulnerability. To secure your system, it is strongly recommended to upgrade to the latest version of FFmpeg. The patch is available in this commit: https://github.com/FFmpeg/FFmpeg/commit/5a13d68eb838e476e235eecf5cd914d0233ab403
Conclusion
Integer overflow vulnerabilities can be found even in widely used and well-maintained projects like FFmpeg. This analysis of CVE-2024-36617 highlights the importance of proper handling of integer overflows and keeping software up-to-date. Enhancing the security of open-source projects is an ongoing process and a shared responsibility. By understanding and addressing vulnerabilities, we can strengthen the overall security ecosystem.
Original References and Further Reading
1. FFmpeg project homepage: https://www.ffmpeg.org/
2. Bug report: https://trac.ffmpeg.org/ticket/9933
3. Patch/commit fixing the vulnerability: https://github.com/FFmpeg/FFmpeg/commit/5a13d68eb838e476e235eecf5cd914d0233ab403
4. Understanding integer overflows: https://owasp.org/www-community/vulnerabilities/Integer_overflow
5. Core Audio Format Specification: https://developer.apple.com/library/archive/documentation/MusicAudio/Reference/CAFSpec/CAF_spec/CAF_spec.html
Timeline
Published on: 11/29/2024 18:15:07 UTC
Last modified on: 12/02/2024 18:15:10 UTC