The NATS official Rust clients are vulnerable to MitM when using TLS.
The common name of the server's TLS certificate is validated against
hostname provided by the server's plaintext
during the initial connection setup phase. A MitM proxy can tamper with
host field's value by substituting it with the common name of a
valid certificate it controls, fooling the client into accepting it.
- The NATS Rust client tries to establish a new connection
- The connection is intercepted by a MitM proxy
- The proxy makes a separate connection to the NATS server
- The NATS server replies with an
- The proxy reads the
INFO, alters the
host JSON field and passes
INFO back to the client
- The 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 given
- The client has been fooled by the MitM proxy into accepting the attacker-controlled certificate
Advisory available under CC0-1.0