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FedoraOperating system · Fedoraproject

CVE-2021-4011

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 SwapCreateRegister 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 high-severity out-of-bounds memory access vulnerability exists in the SwapCreateRegister function of xorg-x11-server, an X11 window system server component. This flaw allows local or remote attackers to potentially read or write beyond allocated buffer boundaries, compromising data confidentiality and integrity while also risking system availability.

MitigationUpgrade xorg-x11-server to version 21.1.2 or later, or version 1.20.14 or later, to patch the out-of-bounds access vulnerability in SwapCreateRegister.

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. Verify xorg-x11-server is installed
    Run 'rpm -qa | grep xorg-x11-server' on Fedora, or 'dpkg -l | grep xorg-x11-server' on Debian, or 'xorg-server --version'/'Xorg -version' to query the X server directly
    Affected if No output means the package is not installed and the system is not affected; if output exists, proceed to version check
  2. Determine installed X server version
    Extract the version number from the package query or from 'Xorg -version' output. On Fedora/Debian, use the package manager output; otherwise, the --version flag typically displays 'X.Org X Server version' followed by the number
    Affected if The version displayed is empty or cannot be determined, preventing a comparison to vulnerable ranges
  3. Compare against vulnerable version ranges
    Check if the installed version falls into any of these vulnerable ranges: < 1.20.14, or = 21.1.0, or = 21.1.1. Safe versions are >= 1.20.14 or >= 21.1.2
    Affected if The installed version matches '< 1.20.14', '21.1.0', or '21.1.1', indicating the system is running a vulnerable version of xorg-x11-server
  4. Confirm the SwapCreateRegister function is in use
    The SwapCreateRegister function is part of the X server's core graphics handling. This function is invoked during X client registration operations. If the X server is running and accepting connections, this code path may be active. No specific user action needed as it's an internal server function
    Affected if The X server is actively running and processing X11 client requests, meaning the vulnerable code could be reached

The system is affected if xorg-x11-server is installed AND the installed version is either less than 1.20.14, or exactly 21.1.0, or exactly 21.1.1, and the X server 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 1.20.14 or later
Fixed in 1.20.14
Interim mitigation

Upgrade xorg-x11-server to version 21.1.2 or later, or version 1.20.14 or later, to patch the out-of-bounds access vulnerability in SwapCreateRegister.

Recommended fix High confidence

xorg-x11-server 1.20.14 or later, or 21.1.2 or later

  1. Check current xorg-x11-server version using: rpm -q xorg-x11-server or dpkg -l xorg-x11-server
  2. For Fedora systems: run 'dnf update xorg-x11-server' to upgrade to the fixed version
  3. For Debian systems: run 'apt update && apt install xorg-x11-server' to upgrade to the fixed version
  4. Verify the installed version meets the fixed release requirements (1.20.14 or later, or 21.1.2 or later)
Caveat Standard X server upgrade; may require restart of X session or system

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
  • Testing4.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,720
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,752.

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-2021-4011 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