#VU34840 Resource exhaustion in waitress - CVE-2020-5236

Vulnerability identifier: #VU34840

Vulnerability risk: Medium

CVSSv4.0: 5.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:P/U:Green]

CVE-ID: CVE-2020-5236

CWE-ID: CWE-400

Exploitation vector: Network

Exploit availability: Yes

Vulnerable software:
waitress
Other software / Other software solutions

Vendor: Pylons Project

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.

Mitigation
Install update from vendor's website.

Vulnerable software versions

waitress: 1.4.2

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

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote authenticated user via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability. However, proof of concept for this vulnerability is available.