Discourse Wildcard Iframe Allowlist Bypass (2026.1.8)
CVE-2026-91132 Published on September 24, 2026
Discourse: Wildcard iframe origin allowlist bypass via authority separators
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.
Vulnerability Analysis
CVE-2026-91132 is exploitable with network access, and requires small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality, with no impact on integrity, and no impact on availability.
Weakness Type
Origin Validation Error
The software does not properly verify that the source of data or communication is valid.
Products Associated with CVE-2026-91132
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Affected Versions
discourse:- Version < 2026.8.0 is affected.
- Version >= 2026.7.0-latest, < 2026.7.2 is affected.
- Version >= 2026.6.0-latest, < 2026.6.3 is affected.
- Version >= 2026.1.0-latest, < 2026.1.8 is affected.