Inefficient Algorithmic Complexity Affecting io.netty:netty-handler package, versions [,4.1.137.Final)[4.2.0.Final,4.2.17.Final)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-JAVA-IONETTY-19652372
- published9 Sept 2026
- disclosed8 Sept 2026
- creditmauriceng98
Introduced: 8 Sep 2026
NewCVE-2026-75596 (opens in a new tab)How to fix?
Upgrade io.netty:netty-handler to version 4.1.137.Final, 4.2.17.Final or higher.
Overview
io.netty:netty-handler is a library that provides an asynchronous event-driven network application framework and tools for rapid development of maintainable high performance and high scalability protocol servers and clients. In other words, Netty is a NIO client server framework which enables quick and easy development of network applications such as protocol servers and clients. It greatly simplifies and streamlines network programming such as TCP and UDP socket server.
Affected versions of this package are vulnerable to Inefficient Algorithmic Complexity in the SniHandler and SslClientHelloHandler process. An attacker can exhaust CPU resources on the event loop by sending a fragmented TLS handshake with a small initial record advertising a large ClientHello length, followed by many tiny fragments. This causes the handler to repeatedly reparse and recopy all accumulated handshake data, resulting in quadratic CPU usage before the handshake completes. This can degrade or stall TLS connection handling for all clients on the affected event loop.