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Vulnerability · Published Mar 19, 2026 · Assigned by GitHub_M

CVE-2026-33393Discourse fixes loose hostname matching in spam host allowlist

Medium 4.3

In plain English

A medium-severity improper access control in discourse from discourse. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 19% of all known vulnerabilities).

Severity (CVSS 3.1)4.3Medium
Exploit odds (30 days)0.3%top 81.1% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

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 (as reported)

VendorProductVersions
discourse discourse >= 2026.1.0-latest, < 2026.1.2>= 2026.2.0-latest, < 2026.2.1= 2026.3.0-latest

Weakness: CWE-284 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

References