CVE-2021-3185: Gst-plugins-bad H264 RCE Vulnerability

CVE-2021-3185 Overview

A stack-based buffer overflow vulnerability was discovered in the GStreamer H264 component of gst-plugins-bad before version 1.18.1. When parsing a malformed H264 header, an attacker can trigger stack memory corruption, potentially leading to code execution. This vulnerability affects multimedia applications that rely on GStreamer for H264 video decoding.

Critical Impact

Remote attackers can exploit this vulnerability by crafting malicious H264 media files to cause stack buffer overflow, memory corruption, and potentially achieve arbitrary code execution on vulnerable systems.

Affected Products

• freedesktop gst-plugins-bad versions prior to 1.18.1

Discovery Timeline

• 2021-01-26 - CVE CVE-2021-3185 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-3185

Vulnerability Analysis

This vulnerability is classified as a buffer overflow (CWE-120) and out-of-bounds write (CWE-787) issue affecting the H264 parser component within the gst-plugins-bad package. The flaw exists in the code responsible for parsing H264 video stream headers, where insufficient bounds checking allows an attacker to write beyond the allocated stack buffer.

When processing specially crafted H264 content, the parser fails to properly validate the size of incoming header data before copying it to a fixed-size stack buffer. This oversight enables attackers to overflow the buffer, overwriting adjacent stack memory including return addresses and saved registers. The vulnerability is particularly dangerous because it can be triggered remotely through network-delivered media content.

Root Cause

The root cause lies in improper validation of H264 header data sizes during the parsing process. The H264 parsing routine in gst-plugins-bad allocates a fixed-size buffer on the stack for processing header information but does not adequately verify that incoming data fits within this allocation before performing memory operations. This classic buffer overflow pattern allows excessive input to corrupt stack memory.

Attack Vector

The vulnerability can be exploited remotely over the network. An attacker can craft a malicious media file or stream containing specially constructed H264 headers. When a victim application using the vulnerable gst-plugins-bad library attempts to parse this content, the overflow condition is triggered. This could occur through:

• Opening a malicious video file in a media player
• Streaming content from an attacker-controlled server
• Processing video through web browsers or applications using GStreamer

The attack requires no user authentication or special privileges, making it particularly accessible to threat actors. The malicious content could be delivered through phishing campaigns, compromised websites, or malicious advertisements containing embedded video.

Detection Methods for CVE-2021-3185

Indicators of Compromise

• Unexpected crashes in applications using GStreamer when processing video content
• Stack smashing detected errors in system logs related to GStreamer processes
• Unusual H264 video files with abnormally large or malformed header structures
• Core dumps indicating stack corruption in gst-plugins-bad components

Detection Strategies

• Monitor application logs for segmentation faults or stack overflow errors in GStreamer-related processes
• Implement file inspection controls to detect malformed H264 media files at network boundaries
• Use memory protection mechanisms (ASLR, stack canaries) to detect exploitation attempts
• Deploy endpoint detection solutions that can identify buffer overflow exploitation patterns

Monitoring Recommendations

• Enable crash reporting for multimedia applications to identify potential exploitation attempts
• Monitor network traffic for suspicious video file downloads or streaming from untrusted sources
• Implement application whitelisting to control which programs can process media files
• Review system logs for repeated crashes in media processing applications

How to Mitigate CVE-2021-3185

Immediate Actions Required

• Upgrade gst-plugins-bad to version 1.18.1 or later immediately
• Restrict processing of untrusted H264 media content until patching is complete
• Implement network-level controls to filter suspicious media file downloads
• Enable available memory protection features (ASLR, DEP/NX, stack canaries) on systems running vulnerable software

Patch Information

The vulnerability has been addressed in gst-plugins-bad version 1.18.1 and later releases. Organizations should update their GStreamer installations to the latest available version. For detailed information about the vulnerability, refer to the Red Hat Bug Report #1917192. Gentoo users can find distribution-specific guidance in the Gentoo GLSA 202208-31 advisory.

Workarounds

• Disable or restrict H264 decoding functionality in GStreamer-based applications if patching is not immediately possible
• Implement application sandboxing to limit the impact of potential exploitation
• Use alternative media processing libraries that are not affected by this vulnerability
• Configure firewalls to block untrusted media content at network perimeters