Improper access control in Discourse - CVE-2026-33393
Published: July 1, 2026
Vulnerability identifier: #VU136131
CSH Severity: Low
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Clear
CVE-ID: CVE-2026-33393
CWE-ID: CWE-284
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Civilized Discourse Construction Kit, Inc.
Affected software:
Discourse
Discourse
Detailed vulnerability description
The vulnerability allows a remote user to bypass spam protection.
The vulnerability exists due to improper access control in the allowed_spam_host_domains check when validating host domains against the allowlist. A remote user can use a crafted domain name with an allowlisted suffix to bypass spam protection.
The issue stems from using suffix-based hostname matching without validating a domain boundary, which can affect enforcement of newuser_spam_host_threshold.
How to mitigate CVE-2026-33393
Install security update from vendor's website.