Denial of Service (DoS) Affecting waitress package, versions [2.1.0,2.1.2)

  • Attack Complexity


  • Availability


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  • snyk-id


  • published

    1 Jun 2022

  • disclosed

    1 Jun 2022

  • credit


How to fix?

Upgrade waitress to version 2.1.2 or higher.


waitress is a production-quality pure-Python WSGI server with very acceptable performance.

Affected versions of this package are vulnerable to Denial of Service (DoS) due to a race condition that may cause early termination when a thread closes a socket while the main thread is about to call select(). This will lead to the main thread raising an exception that is not handled, resulting in the entire application being killed.

Note: Users using waitress behind a reverse proxy server are less likely to have issues if the reverse proxy always reads the full response.


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