ProofreadPage improperly sanitizes multiline styles using Sanitizer::checkCSS

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Summary

CVECVE-2026-39838
StatePUBLISHED
Assignerwikimedia-foundation
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-07 20:16:33 UTC
Updated2026-04-08 21:27:00 UTC
DescriptionImproper 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.

Risk And Classification

Primary CVSS: v4.0 6.9 MEDIUM from c4f26cc8-17ff-4c99-b5e2-38fc1793eacc

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

EPSS: 0.000470000 probability, percentile 0.146360000 (date 2026-04-09)

Problem Types: CWE-79 | CWE-79 CWE-79 Improper neutralization of input during web page generation ('cross-site scripting')

VersionSourceTypeScoreSeverityVector
4.0c4f26cc8-17ff-4c99-b5e2-38fc1793eaccSecondary6.9MEDIUMCVSS: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/C...
4.0CNACVSS6.9MEDIUMCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:L/SI:N/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Confidentiality
Low
Integrity
Low
Availability
None
Sub Conf.
Low
Sub Integrity
None
Sub Availability
None

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Wikimedia Foundation MediaWiki - ProofreadPage Extension affected 1.43 custom Not specified
CNA Wikimedia Foundation MediaWiki - ProofreadPage Extension unaffected 1.43 Not specified
CNA Wikimedia Foundation MediaWiki - ProofreadPage Extension unaffected 1.44 Not specified
CNA Wikimedia Foundation MediaWiki - ProofreadPage Extension unaffected 1.45 Not specified

References

ReferenceSourceLinkTags
gerrit.wikimedia.org/r/q/Idd51e18479b32b7176b43ff74ca1c49d6bdd0628 c4f26cc8-17ff-4c99-b5e2-38fc1793eacc gerrit.wikimedia.org
phabricator.wikimedia.org/T406088 c4f26cc8-17ff-4c99-b5e2-38fc1793eacc phabricator.wikimedia.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: SomeRandomDeveloper (en)

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