dbcve.org
FedoraOperating system · Fedoraproject

CVE-2021-41799

HIGH · 7.5 CVSS v3.1 Published 2021-10-11
Fix available
A fix is available. Upgrade to 1.36.2 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges 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
MediaWiki before 1.36.2 allows a denial of service (resource consumption because of lengthy query processing time). ApiQueryBacklinks (action=query&list=backlinks) can cause a full table scan.

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 ApiQueryBacklinks API module in MediaWiki before 1.36.2 allows attackers to trigger full table scans on the backlinks table via the action=query&list=backlinks parameter, causing excessive database resource consumption and denial of service due to prolonged query processing times.

MitigationUpgrade to MediaWiki 1.36.2 or later which contains the fix; alternatively, add proper database indexes on the backlinks table and implement query timeouts or limits.

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:= 33= 34= 35
MediawikiCMS
Affected:< 1.36.2

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
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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 MediaWiki version
    Access the Special:Version page on your wiki or check the includes/Defines.php file for the $wgVersion variable
    Affected if The installed version is less than 1.36.2 (for example, 1.36.0, 1.35.x, or earlier)
  2. Confirm API module availability
    Attempt to access the API endpoint at /api.php or /w/api.php with the action=query&list=backlinks parameter
    Affected if The API responds and returns results without query timeouts or errors
  3. Check if backlinks table lacks proper indexes
    Examine the backlinks table schema in your database using SHOW CREATE TABLE or DESCRIBE for the table named something like 'page' or 'pagelinks' depending on your MediaWiki configuration
    Affected if The backlinks-related columns lack database indexes, causing full table scans on queries
  4. Test query performance with backlinks API
    Execute a query such as action=query&list=backlinks&bltitle=Main_Page and measure the response time and database load
    Affected if The query takes an unusually long time to complete or causes high database CPU usage

You are affected if MediaWiki version is below 1.36.2 AND the API module is accessible and returning backlinks queries without proper indexing or query limits.

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 1.36.2 or later
Fixed in 1.36.2
Interim mitigation

Upgrade to MediaWiki 1.36.2 or later which contains the fix; alternatively, add proper database indexes on the backlinks table and implement query timeouts or limits.

Recommended fix High confidence

MediaWiki 1.36.2 or later

  1. 1. Back up your MediaWiki database and files before performing any upgrade.
  2. 2. Download MediaWiki 1.36.2 or a later stable release from the official MediaWiki website (https://www.mediawiki.org).
  3. 3. Follow the official MediaWiki upgrade instructions for your specific installation method.
  4. 4. After upgrading, verify that the ApiQueryBacklinks functionality works correctly and that the full table scan issue is resolved.
  5. 5. Test other critical MediaWiki functions to ensure the upgrade did not introduce regressions.

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

Fix this in Fedora Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,176.

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-2021-41799 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