CVE-2026-33393

Name of the Vulnerable Software and Affected Versions Discourse versions prior to 2026.3.0-latest.1 Discourse versions prior to 2026.2.1 Discourse versions prior to 2026.1.2

Description Discourse is an open-source discussion platform. The allowed spam host domains check utilized String#end with? without proper domain boundary validation. This allowed domains, such as attacker-example.com, to circumvent spam protection when example.com was allowlisted. The issue stemmed from a lack of requirement for an exact match or a proper subdomain match (preceded by .) to prevent suffix-based bypass of newuser spam host threshold.

Recommendations Update to Discourse version 2026.3.0-latest.1 or later. Update to Discourse version 2026.2.1 or later. Update to Discourse version 2026.1.2 or later.