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Enterprise LinuxOperating system · Redhat

CVE-2025-26595

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 buffer overflow flaw was found in X.Org and Xwayland. The code in XkbVModMaskText() allocates a fixed-sized buffer on the stack and copies the names of the virtual modifiers to that buffer. The code fails to check the bounds of the buffer and would copy the data regardless of the size.

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 · moderate confidence

A stack-based buffer overflow vulnerability exists in the XkbVModMaskText() function within X.Org and Xwayland. The function allocates a fixed-size buffer on the stack and copies virtual modifier names into it without validating the buffer size, allowing an attacker to overwrite adjacent memory by providing excessively long modifier names.

MitigationApply the vendor patch for CVE-2025-26595 which adds proper bounds checking to the XkbVModMaskText() function. Until a patch is available, limit access to keyboard configuration utilities and monitor for unusual X11/Xwayland crash logs.

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. Identify installed X.Org X Server version
    Run 'Xorg -version' or check the installed package version with 'rpm -q xorg-x11-server' (RHEL) or 'dpkg -l xserver-xorg-core' (Debian)
    Affected if Version is lower than 21.1.16
  2. Identify installed Xwayland version
    Run 'Xwayland --version' or check the package version with 'rpm -q xwayland' (RHEL) or 'dpkg -l xwayland' (Debian)
    Affected if Version is lower than 24.1.6 and Xwayland is in use
  3. Identify installed TigerVNC version
    Run 'vncserver -version' or check the package version with 'rpm -q tigervnc' (RHEL) or 'dpkg -l tigervnc-standalone-server' (Debian)
    Affected if TigerVNC is installed (all versions are affected)
  4. Check if X keyboard extension (Xkb) with virtual modifiers is in use
    Examine X configuration files (/etc/X11/xorg.conf, ~/.xkb or active Xkb symbols) for virtual modifier definitions using 'xkbcomp' or review X log files for Xkb initialization messages
    Affected if Virtual modifiers are configured and the Xkb extension is active

You are affected if you are running X Server < 21.1.16, Xwayland < 24.1.6, or any version of TigerVNC, AND the X keyboard extension with virtual modifiers is enabled in your environment.

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 the vendor patch for CVE-2025-26595 which adds proper bounds checking to the XkbVModMaskText() function. Until a patch is available, limit access to keyboard configuration utilities and monitor for unusual X11/Xwayland crash logs.

Recommended fix High confidence

X Server 21.1.16 or later; Xwayland 24.1.6 or later; Red Hat Enterprise Linux updates via RHSA (check access.redhat.com for specific erratum)

  1. 1. Identify the vulnerable package: For RHEL/CentOS, check if xorg-x11-server or xwayland is installed using 'rpm -qa | grep -E "xorg-x11-server|xwayland"'
  2. 2. For Tigervnc, check installed version using 'vncserver -version' or 'rpm -qa | grep tigervnc'
  3. 3. For RHEL systems, apply updates via 'yum update' or 'dnf update' for the affected packages (xorg-x11-server, xwayland, tigervnc)
  4. 4. If specific CVE patches are available from Red Hat, apply them using 'yum update --cve CVE-2025-26595' or download from Red Hat errata
  5. 5. After updating, restart the X server or wayland session for changes to take effect
  6. 6. Verify the fix by checking the updated version matches or exceeds: X Server 21.1.16, Xwayland 24.1.6
Caveat Updating X server components may require restarting the graphical session; verify application compatibility with newer X/Wayland versions before production deployment

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

Fix this in Enterprise Linux Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
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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-2025-26595 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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