Discourse: Wildcard iframe origin allowlist bypass via authority separators

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-91132
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-24 17:17:08 UTC
Updated2026-09-24 17:17:08 UTC
DescriptionDiscourse 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.

Risk And Classification

Primary CVSS: v3.1 4.3 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

Problem Types: CWE-346 | CWE-346 CWE-346: Origin Validation Error

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary4.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
3.1CNADECLARED4.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Discourse Discourse affected < 2026.8.0 Not specified
CNA Discourse Discourse affected >= 2026.7.0-latest, < 2026.7.2 Not specified
CNA Discourse Discourse affected >= 2026.6.0-latest, < 2026.6.3 Not specified
CNA Discourse Discourse affected >= 2026.1.0-latest, < 2026.1.8 Not specified

References

ReferenceSourceLinkTags
github.com/discourse/discourse/commit/d5ae0940707f95da5bc4562f7b544243e3... [email protected] github.com
github.com/discourse/discourse/commit/80968704c1acb1d2ea2c6011dbf6c02ff1... [email protected] github.com
github.com/discourse/discourse/pull/42882 [email protected] github.com
github.com/discourse/discourse/commit/db8064f2a2a2a3feb3308a1c932ac61d95... [email protected] github.com
github.com/discourse/discourse/commit/d88e02ceb2eede4d8b851d9fe8aef753f3... [email protected] github.com
github.com/discourse/discourse/security/advisories/GHSA-4q3q-hph3-3rvp [email protected] github.com
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