Discourse <2026.3.0 domain suffix bypass in allowed_spam_host_domains
CVE-2026-33393 Published on March 19, 2026
Discourse fixes loose hostname matching in spam host allowlist
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.
Vulnerability Analysis
CVE-2026-33393 can be exploited with network access, and requires small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality, with no impact on integrity, and no impact on availability.
Weakness Type
What is an Authorization Vulnerability?
The software does not restrict or incorrectly restricts access to a resource from an unauthorized actor.
CVE-2026-33393 has been classified to as an Authorization vulnerability or weakness.
Products Associated with CVE-2026-33393
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Affected Versions
discourse:- Version >= 2026.1.0-latest, < 2026.1.2 is affected.
- Version >= 2026.2.0-latest, < 2026.2.1 is affected.
- Version = 2026.3.0-latest is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.