[20260908] - Core - XSS in HTML Mail Templates

Project: Joomla!
SubProject: CMS
Impact: Moderate
Severity: Moderate
Probability: Moderate
Versions: 4.0.0-5.4.8,6.0.0-6.1.3
Exploit type: XSS
Reported Date: 2026-08-24
Fixed Date: 2026-09-25
CVE Number: CVE-2026-90918

Description

The mail template feature lacks an escaping mechanism, causing XSS vectors in multiple extensions.

Affected Installs

Joomla! CMS versions 4.0.0-5.4.8, 6.0.0-6.1.3

Solution

Upgrade to version 5.4.9, 6.1.4

Contact

The JSST at the Joomla! Security Centre.

Reported By: Joe Grey / GitHub @StressTestor