CVE-2026-91132: Discourse

Medium severity, CVSS 4.3. EPSS: 0.1% chance of exploitation in the next 30 days.

Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, sites using wildcard patterns in the allowed_iframes setting could accept a crafted iframe URL whose allowlisted suffix appeared after a URL authority separator. The wildcard origin check matched the allowed domain text, while browser URL parsing selected a different attacker-controlled origin. A user with posting privileges could exploit the flaw through a post or a Onebox oEmbed response and cause an attacker-controlled iframe to be rendered independently of the allowlisted domain. Successful exploitation requires a site-configured wildcard iframe pattern and the ability to create a post or trigger an oEmbed request for an attacker-controlled URL. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.

Affected products

• Discourse Discourse: before 2026.8.0 (fixed in 2026.8.0); from 2026.7.0-latest, before 2026.7.2 (fixed in 2026.7.2); from 2026.6.0-latest, before 2026.6.3 (fixed in 2026.6.3); from 2026.1.0-latest, before 2026.1.8 (fixed in 2026.1.8)

Published 2026-09-24. Last modified 2026-09-29.