Eclipse Vert.x WebSocket Decompression Flaw Enables Zip Bomb Denial of Service

Eclipse Vert.x contains a denial of service vulnerability within its WebSocket implementation that stems from uncontrolled memory allocation during decompression. Attackers can exploit this weakness by sending specially crafted compressed frames that expand significantly in size. This behaviour allows malicious actors to exhaust server resources through zip bomb style attacks, effectively denying service to legitimate users. The issue affects the io.vertx:vertx-core component widely used in Java-based microservices and web applications.

Root cause

The vulnerability exists because the WebSocket implementation fails to define a maximum number of bytes for allocation when decompressing frames or messages. Without this upper limit, the system will continue to allocate memory as it processes incoming compressed data. An attacker can send a small compressed payload that expands to consume vast amounts of server memory. This design oversight permits resource exhaustion without any inherent safeguard to stop the expansion process.

Attack path

An attacker initiates the attack by establishing a WebSocket connection to a vulnerable server. They then transmit compressed frames or messages that act as zip bombs. As the server attempts to decompress these inputs, it allocates memory without restriction. The rapid expansion of the data consumes available system resources, leading to service degradation or complete denial of service. No further exploitation steps are required beyond the initial transmission of the compressed payload.

Affected versions

• Eclipse Vert.x 4.0.0 through 4.5.34
• Eclipse Vert.x 5.0.0 through 5.0.12
• Eclipse Vert.x 5.1.0 through 5.1.9
• Eclipse Vert.x 5.2.0

Mitigation

• Monitor for official vendor announcements regarding patches for these versions.
• Implement network level rate limiting on WebSocket connections to reduce the volume of incoming data.
• Configure application level memory limits to restrict the maximum size of decompressed objects.
• Monitor server memory usage for sudden spikes indicative of decompression attacks.

Signals worth monitoring

Teams usually detect this activity by observing unusual memory consumption patterns on servers handling WebSocket traffic. Look for rapid increases in heap usage that do not correlate with normal application load. Check whether specific endpoints are receiving disproportionately small compressed payloads that result in large memory allocations. Alerting on sudden resource exhaustion events can help identify ongoing attacks. Containment moves typically involve isolating affected services and restarting processes to reclaim memory while investigating the source of the malicious traffic.

What to do and how to stay safe: Eclipse Vert.x

• Review current Eclipse Vert.x versions in your deployment to determine if they fall within the affected ranges.
• Monitor server logs for abnormal memory usage spikes during WebSocket connections.
• Implement strict limits on the size of incoming compressed data at the application layer.
• Prepare to apply updates once the vendor provides a confirmed fix for this vulnerability.

Step-by-step guide: Out-of-band patches: what small businesses need to know

General security guidance from the Firewall Pulse newsroom. It is not confirmed advice from the organisations named in this story.

Frequently asked questions

What is the CVSS score for CVE-2026-102467?

The CVSS score is 8.7, which is rated as HIGH severity.

Which component is affected by this vulnerability?

The io.vertx:vertx-core component is affected.

Is there a confirmed fix available yet?

No fix has been confirmed yet in the source material.