CVE-2026-91132

Description

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.

CVSS Vector

References

• https://github.com/discourse/discourse/commit/80968704c1acb1d2ea2c6011dbf6c02ff13238e5
• https://github.com/discourse/discourse/commit/d5ae0940707f95da5bc4562f7b544243e3103f8a
• https://github.com/discourse/discourse/commit/d88e02ceb2eede4d8b851d9fe8aef753f3aa40b9
• https://github.com/discourse/discourse/commit/db8064f2a2a2a3feb3308a1c932ac61d950c9e56
• https://github.com/discourse/discourse/pull/42882
• https://github.com/discourse/discourse/security/advisories/GHSA-4q3q-hph3-3rvp