PostgresNIO processes unencrypted bytes from man-in-the-middle

Any user of PostgresNIO connecting to servers with TLS enabled is vulnerable to a man-in-the-middle attacker injecting false responses to the client’s first few queries, despite the use of TLS certificate verification and encryption.

The remaining text in this section is quoted verbatim from PostgreSQL’s CVE-2021-23222 advisory:

> If more preconditions hold, the attacker can exfiltrate the client’s password or other confidential data that might be transmitted early in a session. The attacker must have a way to trick the client’s intended server into making the confidential data accessible to the attacker. A known implementation having that property is a PostgreSQL configuration vulnerable to CVE-2021-23214. As with any exploitation of CVE-2021-23214, the server must be using trust authentication with a clientcert requirement or using cert authentication. To disclose a password, the client must be in possession of a password, which is atypical when using an authentication configuration vulnerable to CVE-2021-23214. The attacker must have some other way to access the server to retrieve the exfiltrated data (a valid, unprivileged login account would be sufficient).