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Stored XSS in sticky header button messages

Moderate
alistair3149 published GHSA-g955-vw6w-v6pp Oct 17, 2025

Package

Citizen (MediaWiki)

Affected versions

>= 3.3.0 (fbb1d4fe9627281567706f3f6fc99a42ce16fdc4)

Patched versions

>= 3.9.0 (e006923c6dbf113c9a025ca186ecc09fe7b93a15)

Description

Summary

The JS implementation for copying button labels to the sticky header in the Citizen skin unescapes HTML characters, allowing for stored XSS through system messages.

Details

In the copyButtonAttributes function in stickyHeader.js, when copying the button labels, the innerHTML of the new element is set to the textContent of the old element:

mediawiki-skins-Citizen/resources/skins.citizen.scripts/stickyHeader.js

Lines 29 to 41 in f4cbcec

/**
* Copies attribute from an element to another.
*
* @param {Element} from
* @param {Element} to
*/
function copyButtonAttributes( from, to ) {
copyAttribute( from, to, 'title' );
// Copy button labels
if ( to.lastElementChild && from.lastElementChild ) {
to.lastElementChild.innerHTML = from.lastElementChild.textContent || '';
}
}

This unescapes any escaped HTML characters and causes the contents of the system messages to be interpreted as HTML.

PoC

  1. Edit any of the affected messages (citizen-share, citizen-view-history, citizen-view-edit, nstab-talk) to the following payload: <img src="" onerror="alert('Sticky Header Button XSS')">.
  2. Visit any mainpage article in the wiki using the Citizen skin.
image image

Impact

This impacts wikis where a group has the editinterface but not the editsitejs user right. By default, this is the case for the sysop group.

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
High
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N

CVE ID

CVE-2025-62508

Weaknesses

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Learn more on MITRE.

Credits