CVE-2026-33393
Discourse fixes loose hostname matching in spam host allowlist
4.3
MEDIUM
CVSS 3.1
EPSS 0.05%
Description
Discourse is an open-source discussion platform. Prior to versions 2026.3.0, 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, 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.
How to fix CVE-2026-33393
To remediate CVE-2026-33393, upgrade the affected package to a fixed version below.
- —upgrade to 2026.1.2 or later
Is CVE-2026-33393 being exploited?
Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.
Affected packages (1)
- >= 2026.1.0, < 2026.1.2, >= 2026.2.0, < 2026.2.1, >= 2026.3.0, < 2026.3.0
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | MEDIUM4.3 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N |
References (5)
- WEBgithub.com/discourse/discourse/commit/80b19c15fe9c7bc890d1a54f454c8446312ac6d2
- WEBgithub.com/discourse/discourse/commit/d8467b9fbb3d9ed6047b4e508d3fef88a37b8a02
- WEBgithub.com/discourse/discourse/commit/f99099cfbc6b76fe39d6fa2daa48efd69497fb8e
- WEBgithub.com/discourse/discourse/security/advisories/GHSA-95r5-p6qr-hgw6