Medium · published October 15, 2026
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 MySQL client (vertx-mysql-client) pre-allocates an array for column definitions based on a server-declared column count with no upper-bound validation. A malicious or compromised MySQL server, or an attacker with man-in-the-middle positioning, can send a crafted result set packet with an extremely large column count, causing the client to attempt a massive heap allocation. The resulting OutOfMemoryError crashes the Netty event loop thread, causing a complete denial of service for all connections and verticles in the Vert.x application.
The impacted component is io.vertx:vertx-mysql-client.
| Product | Versions | Fixed in |
|---|---|---|
| eclipse/vert.x | ≥ 4.5.0, < 4.5.35 | 4.5.35 |
| eclipse/vert.x | ≥ 5.0.0, < 5.1.10 | 5.1.10 |
| eclipse/vert.x | all versions | — |