Netty prior 4.1.137.Final/4.2.17.Final SslClientHelloHandler SslClientHelloHandler.java io.netty.handler.ssl.SslClientHelloHandler.decode resource consumption

Summaryinfo

A vulnerability was found in Netty. It has been rated as problematic. This impacts the function io.netty.handler.ssl.SslClientHelloHandler.decode of the file handler/src/main/java/io/netty/handler/ssl/SslClientHelloHandler.java of the component SslClientHelloHandler. Performing a manipulation results in resource consumption. This vulnerability is known as CVE-2026-75596. Remote exploitation of the attack is possible. No exploit is available.

Detailsinfo

A vulnerability classified as problematic has been found in Netty. This affects the function io.netty.handler.ssl.SslClientHelloHandler.decode of the file handler/src/main/java/io/netty/handler/ssl/SslClientHelloHandler.java of the component SslClientHelloHandler. The manipulation with an unknown input leads to a resource consumption vulnerability. CWE is classifying the issue as 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. This is going to have an impact on availability. The summary by CVE is:

Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Final and 4.2.17.Final, the default io.netty.handler.ssl.SniHandler constructors use the pre-handshake ClientHello aggregation path in handler/src/main/java/io/netty/handler/ssl/SslClientHelloHandler.java at io.netty.handler.ssl.SslClientHelloHandler#decode, where handshakeBuffer.clear() and writeBytes() recopy all previously received body bytes for every additional TLS record. An unauthenticated remote peer can advertise a large ClientHello and deliver its body in thousands of tiny records, causing quadratic CPU work on the event loop before the TLS handshake completes and degrading TLS handling for other clients. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.

It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2026-75596 since 08/18/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1499 according to MITRE ATT&CK.

Upgrading to version 4.1.137.Final or 4.2.17.Final eliminates this vulnerability.

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Productinfo

Name

• Netty

Website

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

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