CVE-2026-33393: Discourse

Medium severity, CVSS 4.3. EPSS: 0.3% chance of exploitation in the next 30 days.

Discourse is an open-source discussion platform. Prior to versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2, the `allowed_spam_host_domains` check used `String#end_with?` without domain boundary validation, allowing domains like `attacker-example.com` to bypass spam protection when `example.com` was allowlisted. Versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 require exact match or proper subdomain match (preceded by `.`) to prevent suffix-based bypass of `newuser_spam_host_threshold`. No known workarounds are available.

Affected products

• Discourse Discourse: from 2026.1.0, before 2026.1.2 (fixed in 2026.1.2); from 2026.2.0, before 2026.2.1 (fixed in 2026.2.1); version 2026.3.0 only

Published 2026-03-19. Last modified 2026-06-17.