Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, the Discourse post sanitizer allowed a stored cross-origin iframe to bypass the allowed_iframes prefix policy when the iframe src contained encoded userinfo. The sanitizer validated a decoded form differently from the stored iframe src, allowing the browser to interpret an attacker-controlled host while the allowlist check accepted the encoded URL as an allowed prefix.
An authenticated user with posting privileges could persist the iframe in a post and cause attacker-controlled cross-origin content to be rendered. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Privileges Required
Low
Basic privileges needed
User Interaction
None
No user interaction needed
Impact Assessment
Confidentiality
Low
Partial data leak
Integrity
Low
Partial data modification
Availability
None
No disruption
CVSS Vector v3.1
Weakness Type (CWE)
Vulnerable Products
discourse:discourse
References 6
https://github.com/discourse/discourse/security/advisories/GHSA-54vw-chv3-wjpv
https://github.com/discourse/discourse/security/advisories/GHSA-54vw-chv3-wjpv
https://github.com/discourse/discourse/pull/42882
https://github.com/discourse/discourse/pull/42882
https://github.com/discourse/discourse/commit/0a8015e6c7a5079981843721494d30c9a…
https://github.com/discourse/discourse/commit/0a8015e6c7a5079981843721494d30c9a91f5415
https://github.com/discourse/discourse/commit/1304b0c04f87534053b0d574ae5a9b9ba…
https://github.com/discourse/discourse/commit/1304b0c04f87534053b0d574ae5a9b9ba13dd590
https://github.com/discourse/discourse/commit/bac7dd1201911851462483271b4567246…
https://github.com/discourse/discourse/commit/bac7dd1201911851462483271b4567246fa1309d
https://github.com/discourse/discourse/commit/fed3a58c48412ce7207b72a4629ddbc44…
https://github.com/discourse/discourse/commit/fed3a58c48412ce7207b72a4629ddbc44482cd64