async-nats vulnerable to TLS certificate common name validation bypass
The NATS official Rust clients are vulnerable to MitM when using TLS.The common name of the server's TLS certificate is validated against the `host`name provided by the server's plaintext `INFO` message during the initial connection setup phase. A MitM proxy can tamper with the `host` field's value by substituting it with the common name of a valid certificate it controls, fooling the client into accepting it.Reproduction stepsThe NATS Rust client tries to establish a new connectionThe connection is intercepted by a MitM proxyThe proxy makes a separate connection to the NATS serverThe NATS server replies with an `INFO` messageThe proxy reads the `INFO`, alters the `host` JSON field and passes the tampered `INFO` back to the clientThe proxy upgrades the client connection to TLS, presenting a certificate issued by a certificate authority present in the client's keychain. In the previous step the `host` was set to the common name of said certificate`rustls` accepts the certificate, having verified that the common name matches the attacker-controlled value it was givenThe client has been fooled by the MitM proxy into accepting the attacker-controlled certificate