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MEDIUM severity

CVE-2020-25812 — core

MEDIUM

CVE-2020-25812 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in mediawiki/core. A fix is available for mediawiki/core — see the affected versions and patch details below.

MediaWiki Cross-site Scripting (XSS) vulnerability

Also known asBIT-mediawiki-2020-25812GHSA-rj9p-8jxj-2ch4
Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Nov 3, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.1%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs66th percentile — riskier than 66% of all scored CVEsHighest risk
0.00%0.53%1.07%1.60%0.4%1.1%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

2 pkgs affected
🐘mediawiki/core🐘mediawiki/core

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

Description

An issue was discovered in MediaWiki 1.34.x before 1.34.4. On Special:Contributions, the NS filter uses unescaped messages as keys in the option key for an HTMLForm specifier. This is vulnerable to a mild XSS if one of those messages is changed to include raw HTML.

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
🐘Packagistmediawiki/core≥ 1.34.0&&< 1.34.31.34.3composer require mediawiki/core:^1.34.3
🐘Packagistmediawiki/core≥ 1.35.0-rc.0&&< 1.35.01.35.0composer require mediawiki/core:^1.35.0

Affected Products

2 products · 2 configurations
OS
fedorafedoraproject
1 version
33
Application
mediawikimediawiki
≥ 1.34.0 && < 1.34.4
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mediawiki/core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update mediawiki/core to 1.34.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-25812 is resolved across your whole dependency graph.

  3. Workarounds

    Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

An issue was discovered in MediaWiki 1.34.x before 1.34.4. On Special:Contributions, the NS filter uses unescaped messages as keys in the option key for an HTMLForm specifier. This is vulnerable to a mild XSS if one of those messages is changed to include raw HTML.
O3 Security · Impact-Aware SCA

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CVE-2020-25812: core XSS — Fixed in 1.34.3