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 steps
- 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
INFO
message - The proxy reads the
INFO
, alters thehost
JSON field and passes the tamperedINFO
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