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CVE-2026-39838 Wikimedia Foundation CVE debrief

CVE-2026-39838 is a cross-site scripting vulnerability in the ProofreadPage Extension of MediaWiki. The issue allows for XSS targeting non-script elements and has been remediated in MediaWiki versions 1.43, 1.44, and 1.45. This vulnerability has a CVSS score of 6.9 and is considered Medium severity. Users of MediaWiki with the ProofreadPage Extension should be aware of this vulnerability and take steps to remediate it.

Vendor
Wikimedia Foundation
Product
MediaWiki - ProofreadPage Extension
CVSS
MEDIUM 6.9
CISA KEV
Not listed in stored evidence
Original CVE published
2026-04-07
Original CVE updated
2026-07-21
Advisory published
2026-04-07
Advisory updated
2026-07-21

Who should care

Users of MediaWiki with the ProofreadPage Extension should be aware of this vulnerability and take steps to remediate it. This includes reviewing and updating input validation and sanitization, monitoring for potential XSS attacks, and considering compensating controls for exposed systems.

Technical summary

The vulnerability is caused by improper neutralization of input during web page generation. This allows for cross-site scripting (XSS) attacks 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. Affected product deployments should be reviewed for exposure and remediated accordingly. Users of MediaWiki with the ProofreadPage Extension should verify their deployments, review input validation and sanitization, and monitor for potential XSS attacks. Defenders should confirm whether affected product deployments exist in managed environments and assign an owner for follow-up, review compensating controls for exposed systems, and track exceptions and retest remediated assets.

Defensive priority

Medium priority due to CVSS score of 6.9

Recommended defensive actions

  • Remediate the vulnerability by updating to a remediated version of MediaWiki
  • Review and update input validation and sanitization
  • Monitor for potential XSS attacks
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record was published on 2026-04-07T20:16:33.477Z and last modified on 2026-07-21T19:10:00.107Z. The NVD entry is currently Awaiting Analysis. This vulnerability affects MediaWiki users with the ProofreadPage Extension. Defenders should verify the affected scope and review input validation and sanitization.

Official resources

AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-04-07T20:16:33.477Z and has not been modified since then. The NVD entry is currently Awaiting Analysis.