CVE-2026-39838 ProofreadPage improperly sanitizes multiline styles using Sanitizer::checkCSS
Attackers can inject malicious scripts via improperly sanitized CSS styles in the ProofreadPage extension, potentially compromising user sessions.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-39838?
CVE-2026-39838 is a medium-severity cross-site scripting vulnerability in Wikimedia Foundation MediaWiki - ProofreadPage Extension, published on 7 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-79
Which versions are affected by CVE-2026-39838?
How do I fix CVE-2026-39838?
No fix has been published for CVE-2026-39838 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-39838 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-39838 exists.
Sources
Also known as GHSA-9jh3-xqmw-83x6.