AdGuard Home, when started with the --glinet flag, contains an authentication bypass vulnerability that allows unauthenticated attackers to gain full admin access by supplying a path traversal sequence in the Admin-Token cookie, exploiting unsanitized string concatenation in the token file path construction within the authglinet middleware. Attackers can craft a request with a traversal payload in the Admin-Token header to redirect file reads to arbitrary paths.

AdGuard Home is a network-wide software for blocking ads and tracking. Prior to 0.107.73, an unauthenticated remote attacker can bypass all authentication in AdGuardHome by sending an HTTP/1.1 request that requests an upgrade to HTTP/2 cleartext (h2c). Once the upgrade is accepted, the resulting HTTP/2 connection is handled by the inner mux, which has no authentication middleware attached. All subsequent HTTP/2 requests on that connection are processed as fully authenticated, regardless of whether any credentials were provided. This vulnerability is fixed in 0.107.73.