CVE-2022-43242 - Heap Buffer Overflow in Libde265 v1..8 Exploited via Crafted Video Files

Libde265 is a widely used open-source library that helps applications decode H.265/HEVC video streams. It's integrated into popular projects, from media players to surveillance devices. In late 2022, security researchers discovered a serious vulnerability in Libde265 version 1..8—tracked as CVE-2022-43242. Through a specially crafted video file, attackers can exploit this flaw to crash applications, causing a Denial of Service (DoS). This long read explains what happened, how the vulnerability works, and how you can recreate and protect against the exploit.

Library: libde265 (v1..8)

- CVE: CVE-2022-43242

Vulnerable function: mc_luma<unsigned char> in motion.cc

- Impact: Denial of Service (application crash); possible staging ground for further exploitation under some conditions

How it Works

At its core, the vulnerability happens during motion compensation while decoding a video frame. The function mc_luma handles pixel data for video frames. If an attacker creates a strangely crafted HEVC file, they can trick the function into writing data outside of the allocated memory buffer ("heap buffer overflow"). This usually results in a program crash, but under some wild conditions, it could even cause memory corruption leading to more serious attacks.

Here's a simplified snippet inspired by the real vulnerable code in motion.cc

template <typename T>
void mc_luma(T* dst, int dst_stride, const T* src, int src_stride, int width, int height) {
    for (int y = ; y < height; ++y) {
        memcpy(dst + y * dst_stride, src + y * src_stride, width * sizeof(T));
    }
}

What's wrong here?

- There are no checks to make sure dst + y * dst_stride stays within the bounds of the allocated buffer.
- If an attacker provides width or height values that are too large, memcpy will happily write past the buffer, corrupting memory.
- The library assumes that the provided src, dst, src_stride, and dst_stride are valid and safe—which may not always be true with a malicious file.

What does an attacker do?

1. Creates a malicious video file with carefully crafted video frame metadata. The metadata will trick the decoder into passing oversized values to mc_luma.

User opens the video in a media app using libde265 v1..8.

3. Libde265 processes the frame and eventually calls mc_luma with maliciously large width or height.
4. Heap buffer overflow occurs. This often leads to an application crash, causing a Denial of Service.

Sample proof-of-concept (PoC) command

Suppose you named your malicious file evil.hevc. You could trigger the crash using the libde265 command-line tool:

$ dec265 evil.hevc
Segmentation fault (core dumped)

That's it! Simply decoding the file is enough for users to crash their player.

Here’s an extremely simplified C++ demonstration based on the issue

#include <iostream>
#include <cstring>

int main() {
    const int safe_width = 16;
    const int safe_height = 16;
    unsigned char* buffer = new unsigned char[safe_width * safe_height];

    // Malicious values (crafted by attacker)
    int attacker_width = 4096; // much larger than buffer
    int attacker_height = safe_height;

    // This memcpy will overwrite heap memory!
    for (int y = ; y < attacker_height; ++y) {
        memcpy(buffer + y * safe_width, buffer, attacker_width); // overflow!
    }

    delete [] buffer;
    return ;
}

Run this, and you’ll likely get a segmentation fault. In real-life libde265, the same logic, combined with a very large video frame size in a HEVC file, triggers the bug.

Mitigation & Official Patch

Status: This issue was patched in later versions (see GitHub issue and commit). The developers added stricter buffer checks and ensured no out-of-bounds writing.

Conclusion

CVE-2022-43242 is a reminder: even old, trusted libraries can hide dangerous bugs. If your software uses libde265 for HEVC decoding, make sure to upgrade. Attackers can and do weaponize tiny errors like this, and a simple video file could crash critical software or devices.

Codecs are complex—and that’s why updates, fuzz-testing, and prompt response to CVEs matter so much. Stay safe, and always patch early!

If you liked this deep dive, share it with your team or other codec users. Responsible disclosure, patching, and careful design keep the ecosystem safe!

Timeline

Published on: 11/02/2022 14:15:00 UTC
Last modified on: 02/27/2023 15:25:00 UTC