CVE-2020-5236

Advisory

Waitress 1.4.2 allows a DOS attack when waitress receives a header that contains invalid characters. When a header like "Bad-header: xxxxxxxxxxxxxxx\x10" 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 behavior required by errata associated with RFC7230. The regular expression that was used to validate incoming headers has been updated in version 1.4.3.

Affected package

Affected versions

Fixed versions

Vulnerability changelog

This vulnerability has no description

Resources

• https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-5236
• https://github.com/Pylons/waitress/security/advisories/GHSA-73m2-3pwg-5fgc
• https://github.com/Pylons/waitress/commit/6e46f9e3f014d64dd7d1e258eaf626e39870ee1f