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, when CLIENT_SESSION_TRACK was negotiated, the OkPacket.parse() and OkPacket.parseWithInfo() paths allocated byte arrays using server-declared lengths for the OK packet info field and session-state variable names and values before confirming that the bytes remained in the packet. A malicious or compromised server, or a machine-in-the-middle attacker, could send a small OK packet declaring a much larger length and repeatedly force attacker-controlled heap allocations before the subsequent copy failed. This could create garbage-collection pressure or an OutOfMemoryError in the client application. 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 sized heap allocations from lengths declared by the server in OK packets before checking that those lengths fit in the packet. A rogue or MitM server can make the client allocate megabytes from a packet of a few bytes.

## Details

When `CLIENT_SESSION_TRACK` is negotiated (the default), an OK packet carries an info field followed by session-state blocks, each tracked variable being sent as a length-encoded name and value. `OkPacket.parse()` and `parseWithInfo()` allocated `new byte[len]` for the info field, the variable name and the value with the server-declared `len`, then copied the packet data into it. The copy failed with an `ArrayIndexOutOfBoundsException` when the packet was shorter, but only after the allocation had taken place.

A server-declared length of 8 MiB in an 18-byte packet was enough to trigger an 8 MiB allocation; the integer-range validation of length-encoded values does not help, since such lengths are valid positive integers.

The fix validates every server-declared length against the remaining packet bytes before any allocation (`ReadableByteBuf.checkLength()` and a bounded `readBytes(int)`), and stops reading the session state at the first inconsistent entry.

## Impact

Availability only: a malicious or compromised server, or a MitM, can drive attacker-controlled heap allocations on every OK packet, creating GC pressure up to `OutOfMemoryError` in the client application. Exploitation requires control of the server si…

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, when CLIENT_SESSION_TRACK was negotiated, the OkPacket.parse() and OkPacket.parseWithInfo() paths allocated byte arrays using server-declared lengths for the OK packet info field and session-state variable names and values before confirming that the bytes remained in the packet. A malicious or compromised server, or a machine-in-the-middle attacker, could send a small OK packet declaring a much larger length and repeatedly force attacker-controlled heap allocations before the subsequent copy failed. This could create garbage-collection pressure or an OutOfMemoryError in the client application. This issue is fixed in versions 3.3.7, 3.4.5, and 3.5.11.