Cross-site scripting in Flarum - CVE-2026-30913
Published: April 20, 2026
Vulnerability identifier: #VU126535
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-2026-30913
CWE-ID: CWE-79
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Flarum
Affected software:
Flarum
Flarum
Detailed vulnerability description
The vulnerability allows a remote user to mislead users into visiting attacker-controlled domains.
The vulnerability exists due to improper neutralization of user-controlled input in plain-text notification emails when inserting a nickname into email content. A remote user can set a specially crafted nickname and trigger a notification email to mislead users into visiting attacker-controlled domains.
The issue is present when the flarum/nicknames extension is enabled, and some email clients may render markdown link syntax while virtually all email clients autolink domain-like nicknames.
How to mitigate CVE-2026-30913
Install security update from vendor's website.