CVE-2026-56000Network attack vector

Heap corruption via dangling GLX context tag

Published Jul 8, 2026 · Updated Jul 8, 2026

Use-after-free in X.Org Server and Xwayland allows remote authenticated users with an X connection to corrupt server heap memory. CommonMakeCurrent() retains a pointer into the per-client contextTags array, reallocates that array for a new tag, then clears five fields through the dangling pointer. A permitted X client can trigger the freed-memory writes with 34 crafted GLX requests; upstream has not demonstrated code execution.

CVSS severity9.0
Critical
EPSS probability0.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in X.Org Server and Xwayland allows remote authenticated users with an X connection to corrupt server heap memory. CommonMakeCurrent() retains a pointer into the per-client contextTags array, reallocates that array for a new tag, then clears five fields through the dangling pointer. A permitted X client can trigger the freed-memory writes with 34 crafted GLX requests; upstream has not demonstrated code execution.

The record

CVE
CVE-2026-56000
Published
Jul 8, 2026
Updated
Jul 8, 2026
Vendor
X.Org
Product
X.Org Server
Classifications
CWE-416, T1068
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 8, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 8, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <21.1.24

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

X.Org · X.Org Serverversion=0 <21.1.24
X.Org · Xwaylandversion=0 <24.1.13

Published CVSS scores

7.8NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
9.0SUSECVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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