CVE-2025-66418
High
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.
SeverityHigh
CVSS7.5
Exploit probability54. percentile0.7%
Product
Python Urllib3
PublishedDec 5, 2025
First seenDec 5, 2025
Weakness typeCWE-770Allocation of resources without limits
How to fix
Update
- python urllib32.6.0 or later
- urllib32.6.0 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| python urllib3 | 1.24 ≤ v < 2.6.0 | 2.6.0 |
| urllib3PyPI | 1.24 ≤ v < 2.6.0 | 2.6.0 |
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