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FedoraOperating system · Fedoraproject

CVE-2021-4008

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 SProcRenderCompositeGlyphs 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 memory corruption vulnerability exists in xorg-x11-server's SProcRenderCompositeGlyphs function. An out-of-bounds access occurs when processing glyph rendering requests in the X11 Render extension, allowing potential memory corruption that could be exploited for local privilege escalation or denial of service.

MitigationUpgrade xorg-x11-server to version 21.1.2 or later, or 1.20.14 or later, depending on the active branch. For systems where upgrading is not immediately feasible, consider restricting X11 access and ensuring appropriate system isolation.

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. Check if xorg-x11-server is installed
    On Fedora/RHEL: rpm -qa | grep xorg-x11-server. On Debian: dpkg -l | grep xorg-x11-server
    Affected if Package is not installed means not affected; if installed, continue to version check
  2. Determine installed xorg-x11-server version
    On Fedora/RHEL: rpm -q xorg-x11-server. On Debian: dpkg -s xorg-x11-server | grep Version
    Affected if Installed version is < 1.20.14 OR equals 21.1.0 OR equals 21.1.1, then vulnerable
  3. Verify X Render extension is enabled
    Check /etc/X11/xorg.conf or examine X server capabilities withxdpyinfo 2>/dev/null | grep -i render
    Affected if The Render extension must be loaded for the vulnerability to be exploitable; if disabled, risk is reduced
  4. Confirm X server is running
    Check for active X11 process: ps aux | grep Xorg or ls /tmp/.X* 2>/dev/null
    Affected if Vulnerability only applies when X server is actively running; if no X server, not immediately exploitable

User is affected if xorg-x11-server version matches the vulnerable ranges (below 1.20.14, or exactly 21.1.0 or 21.1.1) AND the X server with Render extension is 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 1.20.14 or later, depending on the active branch. For systems where upgrading is not immediately feasible, consider restricting X11 access and ensuring appropriate system isolation.

Recommended fix High confidence

X Server 1.20.14 (for 1.20.x branch) or X Server 21.1.2 (for 21.x branch)

  1. Identify the currently installed xorg-x11-server version using: `rpm -qa | grep xorg-x11-server` (Fedora) or `dpkg -l | grep xserver-xorg-core` (Debian)
  2. For Fedora 34/35: Run `sudo dnf update xorg-x11-server` to apply the security patch
  3. For Debian 9/10/11: Run `sudo apt-get update && sudo apt-get upgrade` to apply the security patch
  4. For X Server from source: Upgrade to version 1.20.14 or 21.1.2 (whichever branch is in use)
  5. Restart the X server or reboot the system to apply the update
  6. Verify the fix by checking the installed version: `xdpyinfo` or checking the package version again

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

Fix this in Fedora Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing3.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,210
Get the upgrade done

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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-2021-4008 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