Glances is an open-source system cross-platform monitoring tool. Glances recently added DNS rebinding protection for the MCP endpoint, but prior to version 4.5.2, the main REST/WebUI FastAPI application still accepts arbitrary Host headers and does not apply TrustedHostMiddleware or an equivalent host allowlist. As a result, the REST API, WebUI, and token endpoint remain reachable through attacker-controlled domains in classic DNS rebinding scenarios.

Once the victim browser has rebound the attacker domain to the Glances service, same-origin policy no longer protects the API because the browser considers the rebinding domain to be the origin. This is a distinct issue from the previously reported default CORS weakness. CORS is not required for exploitation here because DNS rebinding causes the victim browser to treat the malicious domain as same-origin with the rebinding target.

Version 4.5.2 contains a patch for the issue.