CVE-2022-43241 - Crashing Libde265 v1..8 with a Malicious HEVC Video (DoS Exploit Explained)

Libde265 is a popular open-source implementation for decoding HEVC (H.265) video. It’s used in several video tools and platforms, valued for its speed and open license. But like all code, it’s not immune to bugs.

In November 2022, a new vulnerability (CVE-2022-43241) was discovered in libde265 v1..8. This bug allows attackers to crash the application by simply tricking it into decoding a specially crafted video file. In this article, we’ll break down how the crash happens, show you how it could be exploited, and give you pointers on reference materials for more study. Whether you’re a developer, a security enthusiast, or just curious — let’s dive in!

What is CVE-2022-43241?

CVE-2022-43241 is a heap buffer problem in libde265 v1..8. The bug was discovered in the SIMD-optimized motion compensation routines, specifically in the function ff_hevc_put_hevc_qpel_v_3_8_sse defined in sse-motion.cc.

Libde265 decodes H.265 (HEVC) video streams.

- A crafted (malicious/faulty) video can trigger an unchecked operation inside a low-level routine optimized for speed.
- If exploited, this causes the player or any software using library to *crash* — which is a Denial of Service (DoS).

No code execution is reported, but depending on how the crash is triggered, information leaks or further exploitation might be possible (that’s speculative, though).

The Vulnerability in Detail

Motion compensation is part of how HEVC (H.265) achieves high video compression: it reuses blocks of pixels from neighboring frames to store only the differences. For speed, libde265 uses SIMD (Single Instruction Multiple Data) operations, like SSE, to process lots of data in parallel.

The vulnerability specifically exists in the function that performs a "quarter-pixel vertical motion compensation" using SSE instructions.

The Code at Fault

The core problem is with how libde265 indexes video buffer data without sufficient boundary checks. Here’s a simplified example (in pseudo-C code) representing the dangerous pattern:

void ff_hevc_put_hevc_qpel_v_3_8_sse(uint8_t *dst, uint8_t *src, int stride, int height) {
    for (int y = ; y < height; y++) {
        // Dangerous read, if src is manipulated or offset is wrong
        __m128i row = _mm_loadu_si128((__m128i *)&src[y * stride]);
        // ... do SSE processing ...
        _mm_storeu_si128((__m128i *)&dst[y * stride], row);
    }
}

If src is a pointer to controlled (malicious) memory, or if the video file triggers a wrong stride or height value, this can cause a buffer overflow or access violation — and boom, the application crashes.

Triggering the Crash: Proof-of-Concept

Security researchers crafted HEVC video files containing frames or settings specifically designed to mess with the boundaries. When processed, libde265 reaches into memory it doesn’t own, leading to a crash.

Say you have a video file called exploit.hevc. Just trying to play or thumbnail it could crash your app:

# Using ffmpeg with libde265
ffmpeg -i exploit.hevc -f null - 

# Or any player using libde265
gnome-photos exploit.hevc

The software may crash, stop responding, or even open up error dialogs.

Here’s what developers saw in bug reports

#  ff_hevc_put_hevc_qpel_v_3_8_sse (dst=..., src=..., stride=..., height=...) at sse-motion.cc:xxx
Segmentation fault (core dumped)

Exploiting CVE-2022-43241

Remember, this is a DoS exploit: The goal is to make trusted software crash or hang. Attackers could drop a video file on a public platform, or email it as an attachment. If your video pipeline uses libde265, even indirectly, you’re at risk.

Minimal Exploit Example

*(Actual crafted file details are typically shared among researchers, so we won’t copy-paste here. Creating a PoC normally requires fuzzing or manual editing of HEVC bitstreams.)*

Mitigation and Patches

Fixed in Later Versions: The libde265 team patched this bug by tightening the boundary checks before loading data via SSE instructions.

Final Thoughts

CVE-2022-43241 is a textbook example of how complex data, like video files, can surface subtle coding mistakes — especially when hand-optimized assembly or SIMD code is involved. Even if you're not writing a video decoder, this shows why regular code audits, fuzz testing, and library updates are key to keeping your software secure.

Always patch, stay alert, and if you’re managing user-uploaded content, validate everything!

*If you liked this breakdown or need more technical guides, shoot me a message or share the article! For hands-on researchers: never run exploit PoCs on production systems, and always respect data privacy.*

Timeline

Published on: 11/02/2022 14:15:00 UTC
Last modified on: 02/27/2023 15:24:00 UTC