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.
References6
- github.com/discourse/discourse/commit/80968704c1acb1d2ea2c6011d…
- github.com/discourse/discourse/commit/d5ae0940707f95da5bc4562f7…
- github.com/discourse/discourse/commit/d88e02ceb2eede4d8b851d9fe…
- github.com/discourse/discourse/commit/db8064f2a2a2a3feb3308a1c9…
- github.com/discourse/discourse/pull/42882
- github.com/discourse/discourse/security/advisories/GHSA-4q3q-hp…
Metrics
- CVSS 3.1
-
4.3
MEDIUM
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N - EPSS — exploit probability
- 0% percentile: 3 · as of 9 November 2026
- CWE
- CWE-346
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.