Denial of Service (DoS) Affecting io.netty:netty-handler package, versions [4.0.20.Final,4.0.28.Final)

  • Attack Complexity


  • Availability


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  • snyk-id


  • published

    17 Jan 2022

  • disclosed

    17 Jan 2022

  • credit


How to fix?

Upgrade io.netty:netty-handler to version 4.0.28.Final or higher.


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 Denial of Service (DoS) in the OpenSslEngine class which does not have a mechanism to reject remotely initiated SSL renegotiation requests. An attacker can exploit this vulnerability by sending a large number of SSL renegotiation requests, causing the application to attempt to process all of them and tying up CPU and memory resources until the application becomes unresponsive or crashed.


Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its intended and legitimate users.

Unlike other vulnerabilities, DoS attacks usually do not aim at breaching security. Rather, they are focused on making websites and services unavailable to genuine users resulting in downtime.

One popular Denial of Service vulnerability is DDoS (a Distributed Denial of Service), an attack that attempts to clog network pipes to the system by generating a large volume of traffic from many machines.

When it comes to open source libraries, DoS vulnerabilities allow attackers to trigger such a crash or crippling of the service by using a flaw either in the application code or from the use of open source libraries.

Two common types of DoS vulnerabilities:

  • High CPU/Memory Consumption- An attacker sending crafted requests that could cause the system to take a disproportionate amount of time to process. For example, commons-fileupload:commons-fileupload.

  • Crash - An attacker sending crafted requests that could cause the system to crash. For Example, npm ws package