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.
Weakness
The product uses a regular expression with an inefficient, possibly exponential worst-case computational complexity that consumes excessive CPU cycles.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Mechanize | Mechanize_project | * | 0.4.6 (excluding) |
| Python-mechanize | Ubuntu | bionic | * |
| Python-mechanize | Ubuntu | focal | * |
| Python-mechanize | Ubuntu | trusty | * |
| Python-mechanize | Ubuntu | upstream | * |
| Python-mechanize | Ubuntu | xenial | * |
Extended Description
Attackers can create crafted inputs that
intentionally cause the regular expression to use
excessive backtracking in a way that causes the CPU
consumption to spike.
Potential Mitigations
Related Attack Patterns
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/