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Cross-site Scripting (XSS)Weakness · CWE-79

CVE-2026-39838

MEDIUM · 6.9 CVSS v4.0 Published 2026-04-07
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
78/100
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
Improper neutralization of input during web page generation ('cross-site scripting') vulnerability in Wikimedia Foundation MediaWiki - ProofreadPage Extension allows XSS Targeting Non-Script Elements. The issue has been remediated on the `master` branch, and in the release branches for MediaWiki versions 1.43, 1.44, and 1.45.

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

Cross-site scripting vulnerability in MediaWiki's ProofreadPage extension allows injection of malicious code through non-script HTML elements (e.g., img, svg, body tags). The vulnerability has been patched in MediaWiki versions 1.43, 1.44, and 1.45.

MitigationUpgrade MediaWiki to version 1.43, 1.44, or 1.45 (or later) to apply the patched code in the ProofreadPage extension.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

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
Authentication
X
User interaction
None
Scope
X

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:L/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

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. Verify ProofreadPage extension is enabled
    Check your MediaWiki's LocalSettings.php or extension.json for 'wfLoadExtension( "ProofreadPage" )' or similar enablement lines. Alternatively, visit Special:Version on your wiki to see if ProofreadPage is listed among installed extensions.
    Affected if ProofreadPage extension is not listed or not enabled means the vulnerability does not apply to your environment.
  2. Determine MediaWiki core version
    Visit Special:Version on your wiki, or check the 'includes/Defines.php' file for the 'MW_VERSION' constant, or run 'php maintenance/includes/ShowRevision.php' if available. Compare the displayed version number against the fixed releases (1.43.x, 1.44.x, 1.45.x).
    Affected if Running MediaWiki versions 1.42 or lower, or any version below the latest available in your supported branch, indicates potential vulnerability.
  3. Check ProofreadPage extension version
    If listed on Special:Version, note the ProofreadPage extension version. If not displayed there, check the extension's 'extension.json' or 'composer.json' file within the ProofreadPage directory for the version number.
    Affected if ProofreadPage version is earlier than the version bundled with MediaWiki 1.43, 1.44, or 1.45.
  4. Identify actively used ProofreadPage content
    Query your wiki's database for pages in namespaces associated with ProofreadPage (typically namespace IDs 250-253 for Page, Index, and related spaces), or search for pages transcluding the 'ProofreadPage' template or using the '<pagelist>' or '<pagequality>' tags.
    Affected if The presence of existing ProofreadPage-indexed content increases exposure; however, even unused but enabled extensions may present risk if input is processed.
  5. Inspect browser for XSS payloads in rendered output
    Create a test page using ProofreadPage functionality with a crafted input containing HTML attribute injection (for example, enter a value like '" onmouseover="alert(1)' in a Page: namespace field and preview or save the page. Observe whether the browser renders this as a raw attribute or if it is properly escaped.
    Affected if The input renders as unescaped HTML or creates functional event handlers (like onmouseover) in the output page source, confirming the XSS vulnerability is present.

Your environment is affected if the ProofreadPage extension is enabled and MediaWiki core version is below 1.43 (or below 1.44/1.45 depending on your branch), with unescaped HTML appearing in ProofreadPage-rendered content.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade MediaWiki to version 1.43, 1.44, or 1.45 (or later) to apply the patched code in the ProofreadPage extension.

Recommended fix High confidence

MediaWiki 1.45 (latest stable release)

  1. 1. Identify current MediaWiki version by checking the `includes/Defines.php` file or the special version page (Special:Version)
  2. 2. Identify ProofreadPage extension version from the `extensions/ProofreadPage` directory
  3. 3. If running MediaWiki 1.43, 1.44, or 1.45, check if the ProofreadPage extension is updated to the latest patch level for that release branch
  4. 4. For fresh installations, use MediaWiki 1.45 (latest stable release with fix)
  5. 5. For existing installations, upgrade to the appropriate branch (1.43.x, 1.44.x, or 1.45.x) ensuring ProofreadPage extension is also updated
  6. 6. Verify the fix by reviewing the commit on gerrit.wikimedia.org for the ProofreadPage XSS fix
  7. 7. After upgrade, test the ProofreadPage functionality to confirm no regressions
Caveat Minor point release upgrades typically have minimal breaking changes; review the release notes for the specific minor version

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

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA2.0 h
9.0 hours of engineering $1,570
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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-2026-39838 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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