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MEDIUM severity

MediaWiki makeCollapsible allows applying event handler to any CSS selectorGHSA-pfm2-mqwj-ggm5

MEDIUM

GHSA-pfm2-mqwj-ggm5 is a medium-severity (CVSS 5.3) CWE-74 vulnerability in mediawiki/core. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for mediawiki/core — see the affected versions and patch details below.

Also known asBIT-mediawiki-2020-10960CVE-2020-10960
Published
Updated
Affected
3 pkgs
Patched
3 / 3
Exploits
1 known
Exploitation data as of Nov 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.2%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs67th percentile — riskier than 67% of all scored CVEsHighest risk
0.00%0.55%1.10%1.65%0.2%1.2%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

3 pkgs affected
🐘mediawiki/core🐘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

In MediaWiki before 1.34.1, users can add various Cascading Style Sheets (CSS) classes (which can affect what content is shown or hidden in the user interface) to arbitrary DOM nodes via HTML content within a MediaWiki page. This occurs because jquery.makeCollapsible allows applying an event handler to any Cascading Style Sheets (CSS) selector. There is no known way to exploit this for cross-site scripting (XSS).

Affected Packages

3 total 3 fixed
EcosystemPackageVulnerable rangeFix
🐘Packagistmediawiki/core≥ 1.31.0&&< 1.31.71.31.7composer require mediawiki/core:^1.31.7
🐘Packagistmediawiki/core≥ 1.33.0&&< 1.33.31.33.3composer require mediawiki/core:^1.33.3
🐘Packagistmediawiki/core≥ 1.34.0&&< 1.34.11.34.1composer require mediawiki/core:^1.34.1

Affected Products

1 product · 1 configurations
Application
mediawikimediawiki
< 1.34.1
range
Exploits & PoCs
1

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

In MediaWiki before 1.34.1, users can add various Cascading Style Sheets…

phabricator.wikimedia.orgNVDJul 2021

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 1.31.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-pfm2-mqwj-ggm5 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

In MediaWiki before 1.34.1, users can add various Cascading Style Sheets (CSS) classes (which can affect what content is shown or hidden in the user interface) to arbitrary DOM nodes via HTML content within a MediaWiki page. This occurs because jquery.makeCollapsible allows applying an event handler to any Cascading Style Sheets (CSS) selector. There is no known way to exploit this for cross-site scripting (XSS).
O3 Security · Impact-Aware SCA

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MediaWiki makeCollapsible allows applying event handler…