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MediawikiCMS

CVE-2021-31554

MEDIUM · 5.4 CVSS v3.1 Published 2021-04-22
Fix available
A fix is available. Upgrade to after 1.35.2 or later.
See remediation →
60/100
Remediation priority · Elevated
Remotely reachable 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
An issue was discovered in the AbuseFilter extension for MediaWiki through 1.35.2. It improperly handled account blocks for certain automatically created MediaWiki user accounts, thus allowing nefarious users to remain unblocked.

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

The AbuseFilter extension in MediaWiki through 1.35.2 contains a security flaw that fails to properly enforce account blocks on certain automatically created MediaWiki user accounts. This allows blocked users to bypass the block mechanism by leveraging these auto-created accounts, effectively remaining unblocked despite being subject to blocks.

MitigationUpgrade the AbuseFilter extension to version 1.35.3 or later which contains the fix for this block bypass vulnerability. Review existing blocks to ensure they are properly enforced across all account types.

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
MediawikiCMS
Affected:<= 1.35.2

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
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

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

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 MediaWiki version
    Access Special:Version on your wiki, check includes/Defines.php, or query the API action=query&meta=siteinfo to retrieve the installed MediaWiki version number
    Affected if The version number returned is 1.35.2 or lower
  2. Verify AbuseFilter extension is enabled
    Access Special:Version and look for AbuseFilter in the list of installed extensions, or check your LocalSettings.php for a line like require_once 'extensions/AbuseFilter/AbuseFilter.php';
    Affected if AbuseFilter appears in the enabled extensions list
  3. Confirm affected version range
    Compare your identified MediaWiki version against the affected range: any version of MediaWiki up to and including 1.35.2 is vulnerable
    Affected if MediaWiki version is 1.35.2 or any earlier version AND AbuseFilter is active

Your environment is affected if you are running MediaWiki 1.35.2 or earlier with the AbuseFilter extension enabled, as this combination allows the block bypass to be exploited.

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.

From vendor data
Upgrade available Upgrade to a release after 1.35.2
Interim mitigation

Upgrade the AbuseFilter extension to version 1.35.3 or later which contains the fix for this block bypass vulnerability. Review existing blocks to ensure they are properly enforced across all account types.

Fix this in Mediawiki Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
5.0 hours of engineering $860
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,376.

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-2021-31554 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