Vulnerability in Discourse
CVE-2026-33393
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N.
EPSS exploit prediction
EPSS: 0.003 (25.2th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 25th percentile — 25.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: +0.001
Affected products
- Discourse — versions = 2026.3.0-latest, >= 2026.2.0-latest, < 2026.2.1, >= 2026.1.0-latest, < 2026.1.2
Weakness classification (CWE)
References
- github.com/discourse/discourse/security/advisories/GHSA-95r5-p6qr-hgw6 (Vendor Advisory)
- github.com/discourse/discourse/commit/80b19c15fe9c7bc890d1a54f454c8446312ac6d2 (Patch)
- github.com/discourse/discourse/commit/d8467b9fbb3d9ed6047b4e508d3fef88a37b8a02 (Patch)
- github.com/discourse/discourse/commit/f99099cfbc6b76fe39d6fa2daa48efd69497fb8e (Patch)
Frequently asked questions
- What is CVE-2026-33393?
- CVE-2026-33393 is a medium-severity vulnerability in Discourse, classified under Improper Access Control. CVSS score: 4.3/10. Published 2026-03-19.
- How severe is CVE-2026-33393?
- Medium severity. CVSS v3 base score is 4.3 out of 10.