What’s Vulnerable › Vulnerabilities

CVE-2021-32837: mechanize vulnerable to ReDoS

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 28.9% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2023-01-17 · updated 2026-06-17
• Weakness: CWE-1333

Description

mechanize, a library for automatically interacting with HTTP web servers, contains a regular expression that is vulnerable to regular expression denial of service (ReDoS) prior to version 0.4.6. If a web server responds in a malicious way, then mechanize could crash. Version 0.4.6 has a patch for the issue.

Affected products

• python-mechanize mechanize: before 0.4.6 — fixed in 0.4.6

How to fix

Upgrade to a fixed version: python-mechanize mechanize 0.4.6. Check the vendor advisory for mitigations.

References

• https://github.com/python-mechanize/mechanize/blob/3acb1836f3fd8edc5a758a417dd46b53832ae3b5/mechanize/_urllib2_fork.py#L878-L879
• https://github.com/python-mechanize/mechanize/commit/dd05334448e9f39814bab044d2eaa5ef69b410d6
• https://github.com/python-mechanize/mechanize/releases/tag/v0.4.6
• https://lists.debian.org/debian-lts-announce/2023/06/msg00022.html
• https://securitylab.github.com/advisories/GHSL-2021-108-python-mechanize-mechanize/
• https://github.com/python-mechanize/mechanize/blob/3acb1836f3fd8edc5a758a417dd46b53832ae3b5/mechanize/_urllib2_fork.py#L878-L879
• https://github.com/python-mechanize/mechanize/commit/dd05334448e9f39814bab044d2eaa5ef69b410d6
• https://github.com/python-mechanize/mechanize/releases/tag/v0.4.6
• https://lists.debian.org/debian-lts-announce/2023/06/msg00022.html
• https://lists.debian.org/debian-lts-announce/2025/12/msg00028.html
• https://securitylab.github.com/advisories/GHSL-2021-108-python-mechanize-mechanize/

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