Cross-site scripting in Discourse - CVE-2026-27154
Published: July 1, 2026
Vulnerability identifier: #VU136114
CSH Severity: Low
CVSS v4.0: 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/E:U/U:Clear
CVE-ID: CVE-2026-27154
CWE-ID: CWE-79
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Civilized Discourse Construction Kit, Inc.
Affected software:
Discourse
Discourse
Detailed vulnerability description
The vulnerability allows a remote user to execute arbitrary script in a victim's browser.
The vulnerability exists due to cross-site scripting in the post editing feature when rendering a malicious user's full name as raw HTML. A remote user can set a crafted full name and trick another user into editing a post to execute arbitrary script in a victim's browser.
Only instances with display_name_on_posts enabled and prioritize_username_in_ux disabled are vulnerable.
How to mitigate CVE-2026-27154
Install security update from vendor's website.