CVE-2021-31545
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 · uneditedAn issue was discovered in the AbuseFilter extension for MediaWiki through 1.35.2. The page_recent_contributors leaked the existence of certain deleted MediaWiki usernames, related to rev_deleted.
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 confidenceThe AbuseFilter extension for MediaWiki exposes deleted usernames through the page_recent_contributors variable. The rev_deleted feature in MediaWiki is designed to hide usernames of deleted revisions, but the AbuseFilter was leaking whether certain usernames existed, allowing enumeration of deleted user accounts.
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<= 1.35.2CVSS 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
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- Low
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/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 checksWork through these to decide whether this CVE applies to you.
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Check MediaWiki versionAccess the Special:Version page (index.php?title=Special:Version) or run `php maintenance/revision.php` to see the installed MediaWiki version numberAffected if The version listed is 1.35.2 or earlier
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Verify AbuseFilter extension is enabledCheck includes/AbuseFilter.php exists in the installation directory, or look for 'AbuseFilter' in the list on Special:Version page under 'Installed extensions'Affected if The AbuseFilter extension is listed as installed
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Identify AbuseFilter rules using page_recent_contributorsNavigate to Special:AbuseFilter on the wiki (or query the abuse_filter table in the database) and search for any filter rules containing 'page_recent_contributors'Affected if Any active or enabled AbuseFilter rules reference the page_recent_contributors variable
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Confirm rev_deleted feature is in useCheck the revision table in the database for rows where rev_deleted column has bit 1 set (value 1 or higher), or look at Special:Log/delete to see deletion recordsAffected if The wiki has revisions with rev_deleted flag set, meaning deleted usernames exist in the database
A user is affected if their MediaWiki version is 1.35.2 or earlier, the AbuseFilter extension is enabled, and there are AbuseFilter rules using page_recent_contributors while the wiki has deleted revisions with rev_deleted applied.
Generated from the published advisory. Verify against your own configuration.
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 dataUpgrade MediaWiki to version 1.35.3 or later which contains the fix. As a workaround, audit AbuseFilter rules that reference page_recent_contributors to ensure they do not expose sensitive user information.
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,088.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-31545 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-31545 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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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.
- 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