Resource exhaustion in waitress - CVE-2020-5236

Detailed vulnerability description

The vulnerability allows a remote authenticated user to perform a denial of service (DoS) attack.

Waitress version 1.4.2 allows a DOS attack When waitress receives a header that contains invalid characters. When a header like "Bad-header: xxxxxxxxxxxxxxxx10" is received, it will cause the regular expression engine to catastrophically backtrack causing the process to use 100% CPU time and blocking any other interactions. This allows an attacker to send a single request with an invalid header and take the service offline. This issue was introduced in version 1.4.2 when the regular expression was updated to attempt to match the behaviour required by errata associated with RFC7230. The regular expression that is used to validate incoming headers has been updated in version 1.4.3, it is recommended that people upgrade to the new version of Waitress as soon as possible.

How to mitigate CVE-2020-5236

Sources

• https://github.com/Pylons/waitress/commit/6e46f9e3f014d64dd7d1e258eaf626e39870ee1f
• https://github.com/Pylons/waitress/security/advisories/GHSA-73m2-3pwg-5fgc