Vert.x MySQL Client Heap Exhaustion via Malicious Column Count

Executive Summary

This vulnerability affects the Eclipse Vert.x MySQL client (vertx-mysql-client) in versions 4.0.0 to 4.5.34, 5.0.0 to 5.0.12, 5.1.0 to 5.1.9, and 5.2.0. The client pre-allocates an array for column definitions based on a server-declared column count without validating an upper bound. A malicious or compromised MySQL server, or an attacker with man-in-the-middle access, can send a result set packet with an extremely large column count. This forces the client to attempt a massive heap allocation, leading to an OutOfMemoryError that 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.

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Detection Guidance

Monitor for crashes in Vert.x applications using the MySQL client, particularly OutOfMemoryError logs in Netty event loop threads. Check for unusually large column counts in MySQL result sets by inspecting network traffic or server responses.

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Impact Analysis

This vulnerability can cause a complete denial of service for your Vert.x application. If exploited, it crashes the Netty event loop thread due to an OutOfMemoryError, halting all connections and verticles. This means your application will become unresponsive and unavailable to users.

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Mitigation Strategies

Upgrade the vertx-mysql-client to patched versions (5.2.1, 5.1.10, or 4.5.35). If upgrading is not possible, restrict network access to MySQL servers or use trusted connections to prevent man-in-the-middle attacks.

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