In Eclipse Vert.x versions [4.0.0, 4.5.34] or [5.0.0,5.0.12] or [5.1.0,5.1.9] or [5.2.0, 5.2.0], the Vert.x DB2 client (vertx-db2-client) contains DRDA protocol handling code that deserializes User Defined Type (UDT) column data using a bare ObjectInputStream.readObject() call with no ObjectInputFilter or class allowlist. This code path is triggered when a DRDA server sends a result set with a column tagged as UDT (FDOCA protocol LID 0x50). However, DB2 does not support this type of UDT. The FDOCA 0x50 type is never sent by a legitimate DB2 server. Nevertheless, a malicious or man-in-the-middle DRDA server could craft a response with a 0x50-tagged column, causing the client to deserialize arbitrary attacker-controlled bytes on the Vert.x event loop before any application code can inspect or reject the data. If a Java deserialization gadget chain is present on the application's classpath, this enables remote code execution. Without a gadget chain, denial of service is possible via crafted object graphs. TLS is disabled by default, making man-in-the-middle exploitation feasible. The impacted component is io.vertx:vertx-db2-client.