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MEDIUMpublic exploit

CVE-2020-5236

CVE-2020-5236 — Catastrophic backtracking in regex allows Denial of Service in Waitress

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.

Published Updated Sources: cvelistV5, GitHub_M

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Exploit code

public exploit, none observed

EPSS

2%

chance of exploitation in 30 days

Affects

pylons

waitress

CVSS base

5.7

MEDIUM

Affected scope

The catalog records vendors and products as separate lists, not pairs, so which product belongs to which vendor is not something this page can say.

Vendors (1)

pylons

Products (1)

waitress

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactSource
5.7CVSS 3.1MEDIUM——cvelistV5

Weakness & attack patterns

  • CWE-400

Attack patterns reported against this CVE. The ATT&CK techniques below are inferred from its weakness class.

  • T1499Endpoint Denial of Service

Public exploit

Capability, not use: code existing is a different claim from anyone running it.

Indexed by

poc in github

References

2 on the record

Elsewhere on this site

  • pylonsevery CVE for this vendor
  • CWE-400other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.