Discourse is an open-source discussion platform. From versions 2026.1.0-latest to before 2026.1.3, 2026.2.0-latest to before 2026.2.2, and 2026.3.0-latest to before 2026.3.0, the enter action in StaticController reads the sso_destination_url cookie and redirects to it with allow_other_host: true without validating the destination URL. While this cookie is normally set during legitimate DiscourseConnect Provider flows with cryptographically validated SSO payloads, cookies are client-controlled and can be set by attackers. This issue has been patched in versions 2026.1.3, 2026.2.2, and 2026.3.0.
https://meta.discourse.org/t/using-discourse-as-a-sso-provider/32974
https://meta.discourse.org/t/use-discourse-as-an-identity-provider-sso-discourseconnect/32974
https://github.com/discourse/discourse/security/advisories/GHSA-378j-ccw4-4fwh
https://github.com/discourse/discourse/commit/080408b93d00305b51d71f63f755f43fa601884d
Published: 2026-03-31
Updated: 2026-04-03
Base Score: 6.4
Vector: CVSS2#AV:N/AC:L/Au:N/C:P/I:P/A:N
Severity: Medium
Base Score: 6.1
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Severity: Medium
Base Score: 5.1
Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:A/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N
Severity: Medium
EPSS: 0.00039