EUVD-2026-17546
CVSS 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
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Description
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.
Analysis
Open redirect vulnerability in Discourse versions 2026.1.0 through 2026.3.0 allows unauthenticated remote attackers to redirect users to arbitrary destinations via a malicious sso_destination_url cookie, exploiting a lack of URL validation in the StaticController enter action. While the cookie is normally set during legitimate DiscourseConnect Provider flows with cryptographic validation, attackers can directly set client-controlled cookies to bypass validation logic. …
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