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 side of the connection; no authentication bypass, confidentiality or
integrity impact.

Credit

Reported by fg0x0

References

• GHSA-h599-m3w5-9m7x
• https://nvd.nist.gov/vuln/detail/CVE-2026-119276
• mariadb-corporation/mariadb-connector-j@b9e1ee8
• mariadb-corporation/mariadb-connector-j@beb445f
• mariadb-corporation/mariadb-connector-j@ea8c7b6
• https://github.com/mariadb-corporation/mariadb-connector-j/releases/tag/3.3.7
• https://github.com/mariadb-corporation/mariadb-connector-j/releases/tag/3.4.5
• https://github.com/mariadb-corporation/mariadb-connector-j/releases/tag/3.5.11