CVE-2026-55857

Summary

When PAM (dialog) authentication is used, the connector can be coerced into sending the account password in cleartext over an insecure connection. A hostile or man-in-the-middle server can trigger this with the default configuration, disclosing the user's password.

Details

The mysql_clear_password plugin is gated behind a secure connection: the driver refuses to transmit the password in cleartext over plain TCP. The sibling PAM plugin handler (SendPamAuthPacketFactory, server-side plugin name dialog) did not override that gate and inherited the default value false, so it was not subject to the same secure-transport requirement.

As a result, a hostile or man-in-the-middle server can issue an Authentication Switch Request for the dialog plugin over plain TCP, and the driver responds with the user's password in cleartext. With the default configuration (sslMode=DISABLE, restrictedAuth=null) this is reachable with no non-default options.

Am I affected?

You are affected if all of the following hold:

• You use mariadb Connector/J at a version below the patched release(s).
• Connections can occur over an insecure transport — i.e. plain TCP (sslMode=DISABLE), or a TLS mode that establishes server identity only via self-signed-certificate fingerprint validation.
• An attacker can occupy an on-path (MITM) position, or otherwise cause the client to connect to a server they control, and present an Authentication Switch Request for the dialog plugin.

Connections over properly verified TLS or a local Unix socket are not exposed to this vector.

Impact

Disclosure of the authenticating account's password in cleartext to an on-path or hostile server. The captured credentials can then be reused to authenticate to the database.

Patches

Fixed in 2.7.14, 3.3.5, 3.4.3, and 3.5.9. Upgrade to the patched release on your branch (3.5.x → 3.5.9, 3.4.x → 3.4.3, 3.0/3.1/3.2/3.3.x → 3.3.5, 2.x → 2.7.14). PAM (dialog) is now treated exactly like mysql_clear_password: it may only run over a secure transport. SendPamAuthPacketFactory overrides the secure-required flag to true, and the authentication dispatcher permits a secure-required plugin only when the connection is TLS or a local Unix socket. The pre-existing check that blocks non-MITM-proof plugins when server identity relies solely on self-signed-certificate fingerprint validation continues to apply. Net effect: PAM is allowed over TLS or a Unix socket, and rejected over plain TCP or fingerprint-only connections.

Workarounds

If you cannot upgrade immediately:

• Connect over verified TLS (set sslMode=verify-full) so a man-in-the-middle cannot impersonate the server, or use a local Unix socket.
• Restrict the permitted authentication plugins via restrictedAuth so dialog cannot be negotiated over an insecure transport.

Credit

Reported by Yalguun Tumenkhuu (@fg0x0).