MariaDB's connector leaks the cleartext password to an MitM despite `ssl: true`

Summary

When SSL/TLS is enabled but no CA / server certificate is provided, the connector verifies the server's identity using fingerprint validation. The check is effective, the connection is ultimately rejected when it fails, but it happens after the authentication exchange. As a result, the credentials are sent before validation occurs, so an active man-in-the-middle who presents their own certificate receives the password in the handshake before the connection is aborted.

Impact

The credentials are transmitted to the peer before the server's identity is validated. An on-path attacker (MitM) presenting any certificate can capture the account password, even though the connection then fails the fingerprint check and is closed. The disclosed credentials can subsequently be used to authenticate directly against the server.

• Attacker requirement: active man-in-the-middle position on the network path
• Affected configuration: SSL/TLS enabled without a CA / server certificate

Affected versions

• < 3.2.4
• 3.3.0 – 3.3.2
• 3.4.0 – 3.4.5
• 3.5.0 – 3.5.2

Patches

Fixed in 3.2.4, 3.3.3, 3.4.6, and 3.5.3. Upgrade to one of these (or later) on your branch.

Workarounds

Until you can upgrade, configure certificate verification explicitly, provide the server/CA certificate and use a verifying SSL mode (e.g. VERIFY_CA / VERIFY_FULL).

Reported by haaahaaahiihiiii (no GitHub account).