Netty up to 4.1.137.Final/4.2.17.Final WebSocketServerExtensionHandler resource consumption

Summaryinfo

A vulnerability categorized as problematic has been discovered in Netty up to 4.1.137.Final/4.2.17.Final. Affected is an unknown function of the component WebSocketServerExtensionHandler. Such manipulation leads to resource consumption. This vulnerability is traded as CVE-2026-100658. The attack may be launched remotely. There is no exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in Netty up to 4.1.137.Final/4.2.17.Final and classified as problematic. Affected by this issue is an unknown functionality of the component WebSocketServerExtensionHandler. The manipulation with an unknown input leads to a resource consumption vulnerability. Using CWE to declare the problem leads to CWE-400. The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources. Impacted is availability. CVE summarizes:

Netty (io.netty:netty-codec-http) contains an unbounded per-connection queue in WebSocketServerExtensionHandler. The handler offers an entry to its per-channel validExtensions queue for every inbound HttpRequest, but polls an entry only when the application writes an HttpResponse, and the queue size is never bounded. A remote, unauthenticated peer can use HTTP/1.1 pipelining to send requests faster than the application produces responses — including plain non-upgrade HTTP requests to any path — causing the queue to grow without limit until the JVM exhausts heap memory and terminates with OutOfMemoryError. Because the affected handler is the base class of WebSocketServerCompressionHandler, any server that enables permessage-deflate is exposed on its plain HTTP port before any WebSocket upgrade completes and before any application-level authentication. Affected versions are 4.1.88.Final through 4.1.137.Final and 4.2.0.Final through 4.2.17.Final; the issue is fixed in 4.1.138.Final and 4.2.18.Final.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-100658 since 09/26/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1499.

Upgrading to version 4.1.138.Final or 4.2.18.Final eliminates this vulnerability.

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Productinfo

Name

• Netty

Version

• 4.1.137.Final
• 4.2.17.Final

Website

• Product: https://github.com/netty/netty/

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