CVE-2020-5236

Catastrophic backtracking in regex allows Denial of Service in Waitress

Description

Waitress version 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 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.

Category

5.7
CVSS
Severity: Medium
CVSS 3.1 •
CVSS 2.0 •
EPSS 15.50% Top 10%
Third-Party Advisory github.com Third-Party Advisory github.com
Affected: Pylons Waitress
Published at:
Updated at:

References

Link Tags
https://github.com/Pylons/waitress/security/advisories/GHSA-73m2-3pwg-5fgc third party advisory
https://github.com/Pylons/waitress/commit/6e46f9e3f014d64dd7d1e258eaf626e39870ee1f third party advisory patch

Frequently Asked Questions

What is the severity of CVE-2020-5236?
CVE-2020-5236 has been scored as a medium severity vulnerability.
How to fix CVE-2020-5236?
To fix CVE-2020-5236, make sure you are using an up-to-date version of the affected component(s) by checking the vendor release notes. As for now, there are no other specific guidelines available.
Is CVE-2020-5236 being actively exploited in the wild?
It is possible that CVE-2020-5236 is being exploited or will be exploited in a near future based on public information. According to its EPSS score, there is a ~15% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2020-5236?
CVE-2020-5236 affects Pylons Waitress.
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