MariaDB Connector/J is used to connect applications developed in Java to MariaDB and MySQL databases. From 3.0.0 until 3.3.7, 3.4.5, and 3.5.11, the connector assumed result bytes were UTF-8 but guarded only changes to character_set_client. It did not reject non-UTF-8 character_set_results changes and relied on the server's global session_track_system_variables configuration to report character-set changes. A malicious or compromised server, or a machine-in-the-middle attacker, could suppress tracking or change the result charset so application strings differed from the returned bytes, potentially defeating application-side validation or escaping that depended on the decoded values. This issue is fixed in versions 3.3.7, 3.4.5, and 3.5.11.

Affected: Maven: org.mariadb.jdbc:mariadb-java-client

## Summary

MariaDB Connector/J decodes every result as UTF-8 and guards `character_set_client` against a change to another charset, but did not guard `character_set_results`, and relied on the server's global `session_track_system_variables` list to be told about charset changes at all.

## Details

The connector learns about session variable changes through session tracking, and closes the connection when `character_set_client` is switched away from UTF-8, so that its UTF-8 decoding stays correct. Two gaps remained:

- `character_set_results` was not guarded: a server could switch it to another charset, after which the bytes of every result were decoded as UTF-8 although encoded otherwise. - the list of tracked variables came from the server's global `session_track_system_variables`: a server configured, or made, not to track the character set variables could change them silently.

The fix requests an explicit session tracking list that includes both character set variables whatever the server's global setting, and closes the connection when `character_set_results` is changed to a charset other than `utf8`, `utf8mb3` or `utf8mb4`, as it already did for `character_set_client`.

## Impact

Integrity: a malicious or compromised server, or a MitM, can make the strings an application reads differ from the bytes the server returned (inappropriate encoding for the output context), which can defeat application-side validation or escaping built on those values. Exploitation…

Affected: Ubuntu:18.04:LTS: mariadb-connector-java, Ubuntu:20.04:LTS: mariadb-connector-java, Ubuntu:22.04:LTS: mariadb-connector-java, Ubuntu:24.04:LTS: mariadb-connector-java, Ubuntu:26.10: mariadb-connector-java, Ubuntu:26.04:LTS: mariadb-connector-java

MariaDB Connector/J is used to connect applications developed in Java to MariaDB and MySQL databases. From 3.0.0 until 3.3.7, 3.4.5, and 3.5.11, the connector assumed result bytes were UTF-8 but guarded only changes to character_set_client. It did not reject non-UTF-8 character_set_results changes and relied on the server's global session_track_system_variables configuration to report character-set changes. A malicious or compromised server, or a machine-in-the-middle attacker, could suppress tracking or change the result charset so application strings differed from the returned bytes, potentially defeating application-side validation or escaping that depended on the decoded values. This issue is fixed in versions 3.3.7, 3.4.5, and 3.5.11.