Denial of Service (DoS) Affecting org.apache.tomcat:tomcat package, versions [10.0.3,10.0.5) [9.0.44,9.0.45) [8.5.64,8.5.65)

  • Attack Complexity


  • Availability


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  • snyk-id


  • published

    13 Jul 2021

  • disclosed

    13 Jul 2021

  • credit


How to fix?

Upgrade org.apache.tomcat:tomcat to version 10.0.5, 9.0.45, 8.5.65 or higher.


org.apache.tomcat:tomcat is an implementation of the Java Servlet, JavaServer Pages, Java Expression Language and Java WebSocket technologies.

Affected versions of this package are vulnerable to Denial of Service (DoS). An error introduced as part of a change to improve error handling during non-blocking I/O meant that the error flag associated with the Request object was not reset between requests. This meant that once a non-blocking I/O error occurred, all future requests handled by that request object would fail. Users were able to trigger non-blocking I/O errors, e.g. by dropping a connection, thereby creating the possibility of triggering a denial of service. Applications that do not use non-blocking I/O are not exposed to this vulnerability.


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