dbcve.org
MediawikiCMS

CVE-2021-44857

MEDIUM · 6.5 CVSS v3.1 Published 2021-12-17
Fix available
A fix is available. Upgrade to 1.35.5 / 1.36.3 or later.
See remediation →
71/100
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 MediaWiki before 1.35.5, 1.36.x before 1.36.3, and 1.37.x before 1.37.1. It is possible to use action=mcrundo followed by action=mcrrestore to replace the content of any arbitrary page (that the user doesn't have edit rights for). This applies to any public wiki, or a private wiki that has at least one page set in $wgWhitelistRead.

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

MediaWiki before versions 1.35.5, 1.36.3, and 1.37.1 contains an authorization bypass vulnerability in the MCR (Multi-Content Revisions) functionality. By chaining the action=mcrundo and action=mcrrestore parameters, an authenticated attacker can replace the content of any arbitrary page, including pages they do not have edit permissions for. This affects any public wiki or private wiki with at least one whitelisted read page.

MitigationUpgrade MediaWiki to version 1.35.5, 1.36.3, 1.37.1 or later to receive the security patch. For private wikis, ensure $wgWhitelistRead is properly secured or removed if not strictly necessary.

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:< 1.35.5>= 1.36.0, < 1.36.3>= 1.37.0, < 1.37.1

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

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/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. Check installed MediaWiki version
    Visit Special:Version on your wiki or check the file includes/Defines.php and look for the MW_VERSION constant
    Affected if The installed version is less than 1.35.5, or between 1.36.0-1.36.2, or between 1.37.0-1.37.0
  2. Confirm MCR (Multi-Content Revisions) is in use
    Check if your wiki uses slot-based revisions by examining page content or database entries in the revision table for multiple slot entries. MCR is enabled by default in affected versions.
    Affected if MCR is enabled and the wiki uses slot-based content storage
  3. Determine if the wiki is public or has read whitelist
    Check your LocalSettings.php for $wgWhitelistRead configuration or examine whether the wiki allows unauthenticated read access (no $wgGroupPermissions restrictions)
    Affected if The wiki is publicly readable (no login required) OR $wgWhitelistRead is configured with at least one page listed
  4. Verify edit permission restrictions
    Check LocalSettings.php for $wgGroupPermissions, specifically whether the 'edit' right is restricted for the user group in question
    Affected if The affected user account can authenticate but lacks edit rights on the target page, yet the vulnerability allows content replacement anyway

You are affected if your MediaWiki version is below the fixed releases AND MCR is enabled AND your wiki is either public or has a read whitelist configured.

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 1.35.5 / 1.36.3 / 1.37.1 or later
Fixed in 1.35.51.36.31.37.1
Interim mitigation

Upgrade MediaWiki to version 1.35.5, 1.36.3, 1.37.1 or later to receive the security patch. For private wikis, ensure $wgWhitelistRead is properly secured or removed if not strictly necessary.

Recommended fix High confidence

Upgrade to MediaWiki 1.35.5, 1.36.3, 1.37.1, or later

  1. Backup the MediaWiki database and all files
  2. Backup the LocalSettings.php configuration file
  3. Test the upgrade in a staging environment first
  4. Download and install MediaWiki version 1.35.5, 1.36.3, 1.37.1, or later from www.mediawiki.org
  5. Replace the existing MediaWiki files with the new version, preserving LocalSettings.php and any custom extensions
  6. Run the update.php maintenance script: php maintenance/update.php
  7. Clear any caching systems (e.g., Memcached, Redis) if used
  8. Verify the installation by logging in and testing page edits
Caveat Standard upgrade precautions apply; review release notes for any configuration or extension changes before deploying to production

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

Fix this in Mediawiki Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA3.0 h
15.0 hours of engineering $2,560
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,096.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2021-44857 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2021-44857 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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