Cross-site scripting in Discourse - #VU166157
Published: November 13, 2026
Vulnerability identifier: #VU166157
CSH Severity: Low
CVSS v4: 5.1 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N]
CVE-ID: N/A
CWE-ID: CWE-79
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote user to spoof content or overlay parts of the page with injected HTML.
The vulnerability exists due to improper neutralization of HTML in Discourse's Chat plugin when wildcard-based watched-word censoring rewrites quoted chat messages after sanitization. A remote user can craft a chat transcript on sites with the Chat plugin enabled and wildcard-containing censored watched words to inject HTML attributes and elements that bypass sanitization.
Affected software
Discourse
Remediation
Install security update from vendor's website.
Discourse - addressed in versions 2026.7.5, 2026.9.2, 2026.10.1