In late 2022, a vulnerability tracked as CVE-2022-43252 was discovered in libde265 v1..8, a popular open-source library for decoding H.265/HEVC video streams. This bug is a heap buffer overflow, occurring in the function put_epel_16_fallback in the file fallback-motion.cc. This post breaks down what that means, why it matters, how an attack could work, and how to stay safe.

What Is libde265?

libde265 is an open-source HEVC (H.265) video codec implementation, used by video players, editors, and streaming software worldwide. Many multimedia applications rely on this library for fast, quality video playback.

Vulnerability: Heap buffer overflow

A heap buffer overflow happens when software writes data past the end of a chunk of memory (buffer) allocated on the heap. If attackers craft a special video file, they can manipulate the program to write data it shouldn’t—possibly causing crashes (Denial of Service, DoS), or worse, executing arbitrary code.

Let’s look at a simplified version of the code in question

void put_epel_16_fallback(pixel *dst, const pixel *src, int dst_stride, int src_stride) {
    for (int i = ; i < 16; i++) {
        for (int j = ; j < 16; j++) {
            dst[j] = some_func(src[j]);  // operation on each pixel
        }
        dst += dst_stride;
        src += src_stride;
    }
}

If dst or src doesn’t actually point to a block of at least 16x16 pixels, this function will write outside the allocated memory. The library doesn’t check buffer sizes—which means a corrupted, intentionally crafted video stream can trigger the bug.

How an Attacker Exploits This

The most common outcome here is a program crash (DoS), but more severe exploits (like arbitrary code execution) could be possible depending on memory layout and usage.

Exploit Steps

1. Create Malicious Video File: The attacker crafts a video file that causes the decoder to allocate smaller buffers than the function expects, or to set up returns so buffers are not safe size.
2. Trigger the Vulnerable Code: The video file is played or processed by any application that uses libde265 v1..8.

Heap Overflow Occurs: Program writes data outside the valid memory range.

4. Result: The program may crash immediately. In some environments, further exploitation could be possible (such as arbitrary code execution).

Proof-of-Concept (PoC)

Here’s a minimal python snippet to create a malformed HEVC file (This file is *not* playable but illustrates how simple it is to make malformed files):

# This does not create a valid video, just an oversimplified idea
with open('exploit.hevc', 'wb') as f:
    f.write(b'\x00\x00\x01\x26')   # NAL unit header for a slice segment
    f.write(b'\x00' * 100)         # Not enough data for buffers

Using ffplay or any video tool using libde265 v1..8 to open this file can hit the bug (if you program the data right).

Warning: Don’t run this on a real system—testing exploits can hurt your machine or others’!

Real-World Impact

- Denial of Service (DoS): Crash applications using libde265, for example, media players or servers.
- Worst-case (Theoretical): RCE (Remote Code Execution), if memory manipulation allows code injection (unverified in this case).

The libde265 team patched this issue after its discovery. See the fix here

- GitHub commit

Update to the latest version (check your Linux distro’s packages or pull from the repo).

References

- CVE-2022-43252 at MITRE
- libde265 official source
- Security exploit example

Final Words

CVE-2022-43252 is a classic case of why buffer checks matter in C and C++ libraries. Even tiny mistakes can compromise entire systems, especially when millions of applications depend on a single video decoder.

If your software or server uses libde265, update *now*. Stay safe!


*This article is exclusive to this post—written simply for easy understanding, with resources and sample codes so you know what to watch out for and how to respond.*

Timeline

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