## Summary
With `SslMode` set to `VerifyCA` or `VerifyFull` with no configured CA certificate, an unvalidated TLS connection is treated as secure and a clear-text password can be sent before the certificate is checked. This can occur when relying on the password to validate a self-signed cert, e.g., MariaDB's [zero-configuration TLS](https://mariadb.com/docs/server/security/encryption/data-in-transit-encryption/zero-configuration-ssl).
## Impact
An attacker who can deploy a man-in-the-middle MySQL proxy presenting any self-signed certificate can capture the plaintext database password of a client that:
- uses `SslMode = VerifyCA` or `VerifyFull`, and
- does not use the `SslCa` connection string option, and
- uses a non-empty password.
The attacker completes the TLS handshake with its own cert, requests a clear-text password authentication scheme (`mysql_clear_password`, or forces the `caching_sha2_password`/`sha256_password` clear-text fallback), and receives the password before the fingerprint check rejects the connection, defeating the man-in-the-middle protection `VerifyFull` is expected to provide.
Not affected: a configured CA (`SslCa`), CA-validated TLS, local connections (Unix socket / loopback), or empty passwords. Using `SslMode` set to `Preferred` or `Required` is out of scope (this is documented as not authenticating the server).
## Workarounds
Provide `SslCa` with `VerifyCA`/`VerifyFull`, use a local/Unix-socket connection, or avoid clear-text authentication.
## References
- https://mariadb.org/mission-impossible-zero-configuration-ssl/