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FedoraOperating system · Fedoraproject

CVE-2021-4009

HIGH · 7.8 CVSS v3.1 Published 2021-12-17
Fix available
A fix is available. Upgrade to 1.20.14 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 flaw was found in xorg-x11-server in versions before 21.1.2 and before 1.20.14. An out-of-bounds access can occur in the SProcXFixesCreatePointerBarrier function. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.

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 buffer out-of-bounds vulnerability exists in xorg-x11-server's XFixes extension, specifically in the SProcXFixesCreatePointerBarrier function. This function, which handles pointer barrier creation for restricting cursor movement, accesses memory beyond allocated buffer boundaries. The flaw affects versions prior to 21.1.2 and 1.20.14, potentially allowing attackers to read or write to sensitive memory regions.

MitigationUpdate xorg-x11-server to version 21.1.2 or 1.20.14 or later to patch the out-of-bounds access vulnerability in the XFixes pointer barrier handling code.

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
FedoraOperating system
Affected:= 34= 35
Debian LinuxOperating system
Affected:= 9.0= 10.0= 11.0
X ServerApplication
Affected:< 1.20.14= 21.1.0= 21.1.1

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 xorg-x11-server version
    Run 'rpm -q xorg-x11-server' (Fedora/RHEL) or 'dpkg -l xorg-x11-server' (Debian) to obtain the installed package version
    Affected if The installed version is less than 1.20.14, or equals 21.1.0 or 21.1.1
  2. Confirm XFixes extension is available
    Check if the XFixes extension is loaded by examining X server logs or running 'xdpyinfo' and looking for 'XFixes' in the extensions list
    Affected if The XFixes extension is listed as available (the vulnerability exists in this extension)
  3. Verify pointer barrier usage context
    Review any custom X configuration files (xorg.conf) or application configurations that may use XFixes pointer barrier functionality to restrict cursor movement
    Affected if Pointer barriers are configured or the XFixesCreatePointerBarrier request is being used (the specific vulnerable code path)

You are affected if xorg-x11-server is installed with a version less than 1.20.14, or exactly version 21.1.0 or 21.1.1, and the XFixes extension is enabled in your X server 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 1.20.14 or later
Fixed in 1.20.14
Interim mitigation

Update xorg-x11-server to version 21.1.2 or 1.20.14 or later to patch the out-of-bounds access vulnerability in the XFixes pointer barrier handling code.

Recommended fix High confidence

xorg-x11-server >= 1.20.14 or >= 21.1.2

  1. For Fedora 34/35: Run 'dnf update xorg-x11-server' to obtain the patched version containing the fix for SProcXFixesCreatePointerBarrier
  2. For Debian 9/10/11: Run 'apt update && apt upgrade xserver-xorg-core' to obtain the patched packages
  3. For X Server installations: Upgrade to xorg-x11-server version 1.20.14 or later for the 1.20.x branch, or version 21.1.2 or later for the 21.1.x branch
Caveat Standard X server upgrade - may require restart of X session; ensure user sessions are saved before updating

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

Fix this in Fedora Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
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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-2021-4009 in production — separate from our analysis above.

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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
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