CVE-2026-12891: GStreamer Information Disclosure Flaw

CVE-2026-12891 Overview

CVE-2026-12891 is an out-of-bounds read vulnerability in the GStreamer gst-plugins-bad package. The flaw resides in the H.266/Versatile Video Coding (VVC) parser, which mishandles a crafted aspect ratio indicator value when processing malformed video streams. An attacker can craft a malicious H.266 video file or stream that triggers a read of up to 8 bytes from adjacent memory. Processing the file with any GStreamer-based application leaks limited memory contents through video metadata. The leaked data may expose sensitive information from the application's address space. The weakness is tracked as CWE-125 Out-of-Bounds Read.

Critical Impact
Attackers can leak up to 8 bytes of adjacent process memory per crafted H.266 stream, exposing potentially sensitive data handled by GStreamer-based media players, browsers, and conferencing applications.

Affected Products

GStreamer gst-plugins-bad H.266/VVC parser component
Applications and frameworks that embed GStreamer for media playback or transcoding
Linux distributions packaging vulnerable gst-plugins-bad builds (see Red Hat advisory)

Discovery Timeline

2026-06-23 - CVE-2026-12891 published to the National Vulnerability Database
2026-06-24 - Last updated in NVD database

Technical Details for CVE-2026-12891

Vulnerability Analysis

The vulnerability exists in the H.266/VVC stream parser shipped with GStreamer's gst-plugins-bad. When the parser encounters a malformed bitstream containing a crafted aspect ratio indicator (aspect_ratio_idc) value, it reads beyond the bounds of the lookup buffer used to map indicator values to sample aspect ratios. The over-read can reach up to 8 bytes of memory adjacent to the lookup table. Those bytes are then returned as video metadata, which downstream code or telemetry can expose to the attacker.

Exploitation requires user interaction, such as opening a file or visiting a page that streams the crafted media. The bug is information disclosure only; it does not corrupt memory, escalate privileges, or affect availability.

Root Cause

The parser trusts an attacker-controlled index without validating it against the size of the aspect ratio table. Because the index is used directly in a fixed-size array lookup, oversized values dereference memory immediately following the table. The missing bounds check is a textbook CWE-125 Out-of-Bounds Read.

Attack Vector

The attack vector is network-based and requires user interaction. An attacker hosts a malicious .vvc or container-wrapped H.266 stream and delivers it through a website, email attachment, chat link, or media share. When a GStreamer-based pipeline parses the stream, the disclosed bytes propagate into metadata structures that the application may render, log, or transmit. Further technical detail is available in the GitLab GStreamer Work Item and the Red Hat Bug Report.

No verified public proof-of-concept code is available. Refer to the upstream tracker for reproduction details once published.

Detection Methods for CVE-2026-12891

Indicators of Compromise

Unexpected .vvc, .h266, or MP4/Matroska files containing H.266 elementary streams delivered from untrusted sources
GStreamer pipelines logging parser warnings related to aspect_ratio_idc or VUI parameters during media decoding
Anomalous outbound transmission of media metadata fields containing non-printable or unexpected byte sequences

Detection Strategies

Inspect media files for H.266 NAL units with aspect_ratio_idc values outside the standard-defined range (0–255 with reserved ranges)
Hunt for processes such as gst-launch-1.0, browser media subprocesses, or conferencing clients invoking h266parse against externally sourced content
Correlate parser crash logs and abnormal exits of GStreamer-linked applications across endpoints

Monitoring Recommendations

Track package inventory for gst-plugins-bad versions on Linux endpoints and servers, flagging hosts running unpatched builds
Monitor egress traffic from media-handling applications for unusual metadata or telemetry payloads following media file processing
Alert on user-initiated downloads of H.266/VVC content from low-reputation domains

How to Mitigate CVE-2026-12891

Immediate Actions Required

Apply the patched gst-plugins-bad package from your Linux distribution as soon as updates are published; consult the Red Hat CVE Detail for vendor-specific availability
Restrict opening of H.266/VVC media from untrusted sources until patches are deployed
Audit applications that statically link or bundle GStreamer and confirm they consume the fixed library version

Patch Information

The upstream fix is being tracked in the GitLab GStreamer Work Item 5109. The fix adds bounds validation on the aspect_ratio_idc value before it indexes the sample aspect ratio table. Distribution-specific patched packages are coordinated through vendor advisories such as the Red Hat Bug Report.

Workarounds

Disable or unregister the h266parse element in GStreamer pipelines that do not require VVC decoding
Use sandboxing such as bubblewrap, firejail, or browser content sandboxes to confine media processes and limit the value of leaked memory
Enforce file-type allowlists at email gateways and web proxies to block H.266/VVC streams from untrusted senders

bash

# Configuration example: blacklist the vulnerable parser element
# until the patched gst-plugins-bad package is installed
export GST_PLUGIN_FEATURE_RANK="h266parse:NONE"

# Verify the installed gst-plugins-bad version on Red Hat-based systems
rpm -q gstreamer1-plugins-bad-free

# Verify on Debian/Ubuntu systems
dpkg -l | grep gstreamer1.0-plugins-bad