Cross-site scripting in Discourse - CVE-2021-41095
Published: September 27, 2021 / Updated: July 1, 2026
Vulnerability identifier: #VU136567
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-2021-41095
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 code in a victim's browser.
The vulnerability exists due to cross-site scripting in error message rendering when displaying blocked watched words containing user input. A remote user can submit crafted input to execute arbitrary script code in a victim's browser.
This only affects sites that have blocked watched words containing HTML tags and have modified or disabled the default Content Security Policy.
How to mitigate CVE-2021-41095
Install security update from vendor's website.