# CVE-2025-66418

## Summary

- **CVE ID:** CVE-2025-66418
- **Severity:** HIGH
- **CVSS Score:** 8.9 (CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H)
- **CWE:** CWE-770
- **Published:** Dec 5, 2025
- **Last Modified:** Mar 13, 2026

## Description

urllib3 is a user-friendly HTTP client library for Python. Starting in version 1.24 and prior to 2.6.0, the number of links in the decompression chain was unbounded allowing a malicious server to insert a virtually unlimited number of compression steps leading to high CPU usage and massive memory allocation for the decompressed data. This vulnerability is fixed in 2.6.0.

## Affected Products

- urllib3 — urllib3 (>= 1.24, < 2.6.0)

## References

- [CNA](https://github.com/urllib3/urllib3/security/advisories/GHSA-gm62-xv2j-4w53)
- [CNA](https://github.com/urllib3/urllib3/commit/24d7b67eac89f94e11003424bcf0d8f7b72222a8)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.68%
- **EPSS Percentile:** 50.4

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._