Warpgate is an open‑source bastion host that enables SSH, HTTPS, and MySQL access. In versions prior to 0.25.5, the single‑sign‑on (SSO) workflow accepts a "next" query parameter sent from the provider start endpoint. The value is later embedded directly into the response generated by the return handler without HTML escaping. An attacker that can influence that parameter can craft a link that, when followed by a logged‑in Warpgate user, causes arbitrary HTML and JavaScript to be executed in the user’s browser session. The code runs with the privileges of the authenticated user, allowing the attacker to read session data, invoke user APIs, and, if the victim is an administrator, use administrator‑level APIs.

The vulnerability affects the warp‑tech:warpgate open‑source bastion host, specifically any release earlier than v0.25.5. The flaw is in the SSO return endpoint of the API, which is part of the warpgate‑protocol‑http source tree. Administrators of any site running a susceptible version should apply the patch or upgrade immediately.

The flaw scores a CVSS of 9.3, indicating a high severity with complete network exposure. The EPSS score is not available, so the current exploitation probability cannot be quantified, but the lack of a KEV listing suggests no widespread public exploitation yet. The likely attack vector is a remote web‑based exploit; an adversary can deliver a malicious link that an active Warpgate user follows, leading to reflected XSS and an open redirect. An attacker who succeeds can hijack the victim’s session and gain API access, including privileged actions if the victim holds admin rights.