In early 2025, security researchers discovered a serious bug tracked as CVE-2025-5283 affecting libvpx—the video codec library used by Google Chrome. This vulnerability occurs in versions of Chrome prior to 137..7151.55, and was classified with medium severity by the Chromium team. Through this use-after-free flaw, a remote attacker could craft an HTML page that exploits heap corruption during video processing in Chrome. In this post, we’ll break down what CVE-2025-5283 is, how it works, and show a simplified example of its exploitation.

What Is libvpx and Why Does It Matter?

libvpx is an open-source library developed by Google that handles VP8/VP9 video decoding—used for playing WebM video content in browsers. Because video is everywhere on the web, bugs in this code are very dangerous, especially when browsers process untrusted videos.

The Details: What’s a Use-After-Free?

A use-after-free (UAF) is a memory bug where a program keeps a pointer to memory it already freed (released), and then mistakenly uses that pointer. This can mess up memory management, cause a crash, or even allow attackers to control what gets executed.

In CVE-2025-5283, a flaw in libvpx allows an attacker to cause UAF by crafting a video stream that, when decoded, confuses Chrome’s memory, leading it to use already-freed memory.

How Can Attackers Exploit It?

- A malicious website could embed a crafted VP8/VP9 video file in a webpage
- When a user visits the site, Chrome (before 137..7151.55) decodes the video using vulnerable libvpx code

Example: Simplified Code Snippet

Here’s a (simplified) C/C++-like code that illustrates what a use-after-free looks like in a decoder:

// Pseudocode — not actual Chrome/libvpx code
VideoFrame* frame = new VideoFrame();
// ... process frame ...
free(frame);  // Frame is deallocated

// Some logic error: code still keeps a pointer to frame...
process_frame(frame);  // Oops! Using already-freed memory

In libvpx, such bugs can be triggered under rare decoding errors or unusual combinations of video frame data, which an attacker can set up in a malicious video.

Target user visits the page in a vulnerable Chrome version

4. As Chrome parses the video, the attacker triggers the bug, possibly achieving code execution in the browser context

HTML Example

<!-- Malicious video triggers heap corruption via libvpx bug in old Chrome -->
<video src="evil.webm" autoplay></video>

Mitigation and Fixes

Google fixed CVE-2025-5283 in Chrome 137..7151.55 by patching libvpx. If you’re running any version lower than this—especially for sensitive tasks—update Chrome immediately.

- Also, consider using site isolation, automatic browser updates, and cautious media handling in high-risk environments.

References

- Chromium Security Advisory (Medium): CVE-2025-5283
- libvpx official releases
- Google Chrome releases

Conclusion

CVE-2025-5283 shows how quickly a video decoding bug can become a web security hazard. Always keep your browser up-to-date, and be cautious with sites that play or process unfamiliar video content. Attackers keep finding creative ways to exploit media—don't make it easy for them!

If you’re a developer using libvpx in your own projects, make sure you’re using the latest patches, and consider using memory-safe languages or tools to help guard against UAF bugs in the future.


Stay safe! If you want to learn more, check the official advisories and patch notes linked above.

Timeline

Published on: 05/27/2025 21:15:23 UTC
Last modified on: 05/31/2025 23:15:20 UTC