CVE-2026-39838 Wikimedia Foundation CVE debrief

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.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.