CVE-2023-5217 - Heap Buffer Overflow in VP8 Encoding in libvpx, Affecting Google Chrome and libvpx: Details, Mitigation, and Exploits

CVE-2023-5217 is a high-severity heap buffer overflow vulnerability in the VP8 encoding implementation of libvpx, a popular video codec library used by Google Chrome and other software implementations. Remote attackers could potentially exploit this vulnerability to cause heap corruption via a specially-crafted HTML page, leading to arbitrary code execution. This vulnerability affects Google Chrome versions prior to 117..5938.132 and libvpx up to 1.13.. The issue has been fixed in Chrome 117..5938.132 and libvpx 1.13.1.

In this article, we will discuss the root cause of the vulnerability, how the exploit works, and the steps that could be taken to mitigate the risks associated with this vulnerability.

Background

VP8 is a video compression format developed by On2 Technologies and later acquired by Google. The format is supported in various web browsers, including Google Chrome, through the libvpx codec library. A vulnerability has been discovered in the VP8 encoding process that could lead to heap buffer overflow, which could be exploited by an attacker to execute arbitrary code on the victim's system.

Vulnerability Details

The issue arises in the VP8 encoding process, specifically in the function encode_frame, which is responsible for encoding a single video frame into the VP8 format. The vulnerability is due to improper handling of input dimensions when processing macroblocks (small regions of the frame).

The following code snippet demonstrates the problematic code in libvpx

void encode_frame(VP8_ENCODER *enc, ...) {
  ...
  for (int y = ; y < enc->height; y += 16) {
    for (int x = ; x < enc->width; x += 16) {
      ...
      encode_macroblock(enc, x, y);
      ...
    }
  }
  ...
}

When the encode_macroblock function is called with the (x, y) coordinates at the edge of the frame, it may result in an out-of-bounds write due to incorrect calculation of the macroblock size. This can cause a heap buffer overflow, leading to heap corruption.

Exploit

A remote attacker can exploit this vulnerability by crafting a malicious HTML page containing a specially-formatted video with carefully designed dimensions to trigger the heap buffer overflow. When a victim navigates to the page and their browser begins to process the video, the heap corruption occurs.

The attacker would need to design the malicious video to cause a specific memory layout that may allow code execution. This can be achieved through various means, such as heap spraying or exploiting other browser vulnerabilities to bypass memory protection mechanisms.

Mitigations

Google has already patched the vulnerability in Chrome 117..5938.132, so users should immediately update to the latest version of the browser. Additionally, libvpx 1.13.1 includes a fix for the issue, and any software that relies on libvpx should be updated to use the most recent version.

You can find the official Chromium security advisory and patch information at the following links

- Chromium Security Advisory
- Google Chrome Security Blog

While waiting for updates, you may also consider disabling VP8 video playback or utilizing a browser extension to block video content from untrusted sources.

Conclusion

CVE-2023-5217 is a critical vulnerability in the VP8 encoding process of libvpx, affecting Google Chrome and other software implementations. Users and developers should update to the latest versions of Chrome and libvpx to protect against this vulnerability. Additionally, users should exercise caution when visiting websites with video content from untrusted sources and consider using a secure browser extension to block malicious content.

Timeline

Published on: 09/28/2023 16:15:00 UTC
Last modified on: 09/29/2023 18:37:00 UTC