CVE-2026-39838Network attack vector

Unauthenticated XSS via multiline CSS sanitizer misuse

Published Apr 7, 2026 · Updated Apr 7, 2026

Cross-site scripting in Wikimedia Foundation MediaWiki ProofreadPage before 1.43 allows remote attackers to execute code through crafted styles. ProofreadPage passes multiline CSS to Sanitizer::checkCSS, which is intended for individual style attributes and accepts unsafe stylesheet constructs. The network path requires no authentication or user interaction, and successful injection can disclose or modify limited page-context data.

CVSS severity6.9
Medium
EPSS probability0.40%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in Wikimedia Foundation MediaWiki ProofreadPage before 1.43 allows remote attackers to execute code through crafted styles. ProofreadPage passes multiline CSS to Sanitizer::checkCSS, which is intended for individual style attributes and accepts unsafe stylesheet constructs. The network path requires no authentication or user interaction, and successful injection can disclose or modify limited page-context data.

The record

CVE
CVE-2026-39838
Published
Apr 7, 2026
Updated
Apr 7, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-79, CAPEC-18, T1059.007
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 7, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 7, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.9Wikimedia FoundationCVSS: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 describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CAPEC-18XSS Targeting Non-Script Elements
T1059.007JavaScript/JScript

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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