dbcve.org
Enterprise LinuxOperating system · Redhat

CVE-2025-26601

HIGH · 7.8 CVSS v3.1 Published 2025-02-25
Fix available
A fix is available. Upgrade to 21.1.16 / 24.1.6 or later.
See remediation →
80/100
Remediation priority · High
Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A use-after-free flaw was found in X.Org and Xwayland. When changing an alarm, the values of the change mask are evaluated one after the other, changing the trigger values as requested, and eventually, SyncInitTrigger() is called. If one of the changes triggers an error, the function will return early, not adding the new sync object, possibly causing a use-after-free when the alarm eventually triggers.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A use-after-free vulnerability exists in X.Org and Xwayland where changing an alarm triggers sequential evaluation of change mask values, calling SyncInitTrigger(). When an error occurs during one of these changes, the function returns early without properly adding the new sync object, leading to a use-after-free condition when the alarm subsequently triggers.

MitigationApply available vendor patches for X.Org and Xwayland that address the improper error handling in the alarm change code path to prevent the use-after-free. Consider restricting alarm creation/modification privileges until patches are applied.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Enterprise LinuxOperating system
Affected:= 7.0= 8.0= 9.0
TigervncApplication
Affected:all versions
X ServerApplication
Affected:< 21.1.16
XwaylandApplication
Affected:< 24.1.6

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed X.org X Server version
    Run 'Xorg -version' or check package version with 'rpm -qa | grep xorg-x11-server' (RHEL) or 'dpkg -l | grep xserver-xorg' (Debian/Ubuntu)
    Affected if Version is lower than 21.1.16
  2. Check installed Xwayland version
    Run 'Xwayland --version' or check package version with 'rpm -qa | grep xwayland' (RHEL) or 'dpkg -l | grep xwayland' (Debian/Ubuntu)
    Affected if Version is lower than 24.1.6
  3. Identify if running Xwayland session
    Check environment variable 'XDG_SESSION_TYPE' or look for Xwayland process with 'ps aux | grep Xwayland'
    Affected if Xwayland is in use and version is vulnerable (see versions above)
  4. Check Red Hat Enterprise Linux version
    Run 'cat /etc/redhat-release' or 'rpm -q redhat-release'
    Affected if Version is 7.0, 8.0, or 9.0 and X components are installed from RHEL repositories
  5. Check if TigerVNC is installed
    Run 'vncserver -version' or 'rpm -qa | grep tigervnc' (RHEL)
    Affected if TigerVNC is installed (all versions affected)
  6. Confirm X server is actively running
    Check for Xorg or Xwayland process with 'ps aux | grep -E "Xorg|Xwayland"' or check display manager status
    Affected if An X server is running - this is required for the vulnerability to be exploitable

You are affected if you run X.org X Server below 21.1.16, Xwayland below 24.1.6, any TigerVNC version, or RHEL 7.0/8.0/9.0 with X components, and the X server/Xwayland is actively running.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 21.1.16 / 24.1.6 or later
Fixed in 21.1.1624.1.6
Interim mitigation

Apply available vendor patches for X.Org and Xwayland that address the improper error handling in the alarm change code path to prevent the use-after-free. Consider restricting alarm creation/modification privileges until patches are applied.

Recommended fix Moderate confidence

X Server 21.1.16 or later; Xwayland 24.1.6 or later; RHEL systems should update via relevant RHSA

  1. Update X Server to version 21.1.16 or later
  2. Update Xwayland to version 24.1.6 or later
  3. For Red Hat Enterprise Linux systems, apply the corresponding Red Hat Security Advisory (RHSA) updates for this CVE
  4. Restart X.org or Xwayland after applying updates

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Enterprise Linux Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing8.0 h
  • Review / QA4.0 h
24.0 hours of engineering $4,160
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Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-26601 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data