CVE-2026-103224 in Vert.x
Summary
by MITRE • 10/15/2026
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 MySQL message decoder aggregates inbound multi-packet payloads into a composite direct-memory buffer without any cumulative size limit. A malicious, compromised, or man-in-the-middle MySQL server can send a continuous stream of packets with the maximum payload length (0xFFFFFF), preventing the end-of-message condition from being reached, causing unbounded direct-memory allocation on the client and leading to an out-of-memory crash. This occurs before authentication completes.
The impacted component is io.vertx:vertx-mysql-client.
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Analysis
by VulDB Data Team • 10/15/2026
Eclipse Vert.x versions ranging from 4.0.0 through 5.2.0 contain a critical resource exhaustion vulnerability within the MySQL client implementation, specifically in the module identified as io.vertx:vertx-mysql-client. This flaw stems from an improper handling of multi-packet payloads during the protocol communication phase between the client and the database server. The underlying technical issue involves the message decoder's logic for aggregating inbound data into a composite direct-memory buffer. In standard MySQL protocol operations, large responses are split across multiple packets that must be reassembled by the client to form a complete response. However, in these affected versions of Vert.x, the implementation fails to enforce any cumulative size limit on this aggregation process. Consequently, if an attacker can influence or intercept the data stream, they can exploit this lack of bounds checking to trigger unbounded memory allocation.
The operational impact of this vulnerability is severe, primarily manifesting as a denial-of-service condition through out-of-memory crashes. A malicious actor, such as a compromised MySQL server, a man-in-the-middle attacker capable of injecting packets into the network stream, or an internal threat agent with access to the database endpoint, can send a continuous stream of packets configured with the maximum allowable payload length of 0xFFFFFF bytes. By doing so, they prevent the end-of-message condition from being reached in the expected manner. Instead of terminating the connection upon receiving sufficient data for a valid response, the client continues to allocate direct memory buffers to accommodate each incoming packet. This unbounded allocation rapidly consumes available heap and off-heap memory resources on the client side, leading inevitably to an out-of-memory error that crashes the application or service relying on the Vert.x MySQL client.
A particularly dangerous aspect of this vulnerability is its occurrence before authentication completes. Because the flaw triggers during the initial phases of protocol negotiation and data reception prior to successful user verification, it does not require valid credentials to be exploited. This significantly lowers the barrier for entry for attackers, allowing them to disrupt service availability without needing to bypass security controls or steal sensitive information first. The attack vector is straightforward yet effective: simply flooding the connection with large packets until the client's memory resources are exhausted.
From a classification perspective, this vulnerability aligns closely with CWE-789, which describes Memory Allocation with Unlimited Resources leading to Denial of Service. It also relates to CWE-400 regarding Uncontrolled Resource Consumption. In terms of adversarial tactics, this behavior is consistent with ATT&CK technique T1499, Endpoint Denial of Service, specifically under the sub-category of resource exhaustion via application layer flooding. The lack of input validation and size constraints on network-received data represents a fundamental failure in secure coding practices for network clients that handle variable-length binary protocols.
To mitigate this risk, organizations using affected versions of Eclipse Vert.x must upgrade to patched releases immediately. For users on the 4.x branch, upgrading to version 4.5.35 or later is required. Similarly, those on the 5.x branches should update to at least 5.0.13 for the 5.0 line, 5.1.10 for the 5.1 line, and 5.2.1 for the 5.2 line. These updates include fixes that enforce strict limits on the size of aggregated multi-packet payloads, ensuring that memory allocation remains bounded regardless of the volume or size of incoming data from the server. Until upgrades can be performed, network-level controls such as firewalls or intrusion prevention systems may help mitigate exposure by limiting packet sizes or detecting anomalous traffic patterns indicative of this specific flooding attack, though application-layer patching remains the definitive remediation strategy.