CVE-2026-33393 Discourse — Exploit & Vulnerability Details MEDIUM

Parameter	Value
CVSS	4.3 (MEDIUM)
Affected Versions	2026.1.0 — 2026.2.1
Fixed In	2026.1.2
Type	CWE-284 (Improper Access Control)
Vendor	Discourse
Public PoC	No

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.

Attack Parameters

Attack Vector

Network

Can be exploited remotely

Attack Complexity

Low

Easy to exploit

Privileges Required

Low

Basic privileges needed

User Interaction

None

No user interaction needed

Impact Assessment

Confidentiality

None

No data leak

Integrity

Low

Partial data modification

Availability

None

No disruption

CVSS Vector v3.1

Weakness Type (CWE)

CWE-284 Improper Access Control

Vulnerable Products 3

Configuration	From (including)	Up to (excluding)
Discourse Discourse cpe:2.3:a:discourse:discourse::::::::	`2026.1.0`	`2026.1.2`
Discourse Discourse cpe:2.3:a:discourse:discourse::::::::	`2026.2.0`	`2026.2.1`
Discourse Discourse cpe:2.3:a:discourse:discourse:2026.3.0::::latest:::	—	—