CVE-2026-33393 — MEDIUM (4.3)

Q: How severe is CVE-2026-33393?

CVE-2026-33393 has been rated MEDIUM with a CVSS base score of 4.3/10. Review the CVSS metrics above for detailed severity breakdown.

Q: Is there a patch for CVE-2026-33393?

Check the references section above for vendor advisories and patch information. Affected products include: Discourse Discourse.

Vulnerability 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.

CVSS Score

4.3

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality

NONE

Integrity

LOW

Availability

NONE

Affected Products

Vendor	Product	Versions
Discourse	Discourse	>= 2026.1.0, < 2026.1.2

Related Weaknesses (CWE)

CWE-284

References

FAQ

What is CVE-2026-33393?

CVE-2026-33393 is a vulnerability with a CVSS score of 4.3 (MEDIUM). 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 vali...

How severe is CVE-2026-33393?

CVE-2026-33393 has been rated MEDIUM with a CVSS base score of 4.3/10. Review the CVSS metrics above for detailed severity breakdown.

Is there a patch for CVE-2026-33393?

Check the references section above for vendor advisories and patch information. Affected products include: Discourse Discourse.