CVE-2026-33393 Discourse fixes loose hostname matching in spam host allowlist
Attackers can bypass spam host restrictions by using domains that loosely match allowlisted entries, allowing spam posts from unauthorized sources.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-33393?
CVE-2026-33393 is a medium-severity vulnerability in Discourse Discourse, published on 19 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.
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.
Weakness: CWE-284
Which versions are affected by CVE-2026-33393?
1 open source package ship an affected version, including discourse. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
discourse Bitnami | From 2026.1.0 | 2026.1.2, 2026.2.1, 2026.3.0 |
Products include Discourse Discourse.
How do I fix CVE-2026-33393?
Upgrade discourse to a fixed version for your release line: 2026.1.2, 2026.2.1 or 2026.3.0.
Is CVE-2026-33393 being exploited?
There is no known exploitation of CVE-2026-33393 in the wild and no public exploit code.
Other vulnerabilities in Discourse Discourse
- CVE-2021-41163 RCE via malicious SNS subscription payload
- CVE-2022-36066 Discourse vulnerable to RCE via admins uploading maliciously zipped file
- CVE-2022-39356 Discourse user account takeover via email and invite link
- CVE-2023-22468 Discourse vulnerable to Cross-site Scripting in local oneboxes
- CVE-2026-27934 Discourse leaks private topic title and post excerpt via user action API endpoint
Sources
Also known as BIT-discourse-2026-33393, GHSA-95r5-p6qr-hgw6.