GHSA-grfq-r75j-rw9x: MariaDB Connector/J: Server could switch character_set_results away from UTF-8 without the client noticing

Summary

MariaDB Connector/J decodes every result as UTF-8 and guards charactersetclient against a change to another charset, but did not guard charactersetresults, and relied on the server's global sessiontracksystemvariables 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 charactersetclient is switched away from UTF-8, so that its UTF-8 decoding stays correct. Two gaps remained:

- charactersetresults 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 sessiontracksystemvariables: 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 charactersetresults is changed to a charset other than utf8, utf8mb3 or utf8mb4, as it already did for charactersetclient.

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 requires control of the server side of the connection; no confidentiality or availability impact.

Credit

Reported by fg0x0