CVSS 4.0
8.9 highCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:HCVE-2025-66418
High (8.9) in python urllib3. EPSS 0.7% chance of exploitation in the next 30 days. Fixed in urllib3 2.6.0.
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.
Severity
CVSS 3.1
7.5 highCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- EPSS
- 0.7% chance of exploitation in the next 30 days; higher than 52% of CVEs (scores of 2026-10-31)
- CWE
- CWE-770
- Published
- Modified
- Record from
- the NVD, synced
Affected
- python:urllib3
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-gm62-xv2j-4w53 | PyPI | urllib3 | >=1.24 <2.6.0 | 2.6.0 |
| PYSEC-2026-1998 | PyPI | urllib3 | >=1.24 <2.6.0 | 2.6.0 |