What is CVE-2025-66418?

CVE-2025-66418 is a high-severity vulnerability in Python Urllib3, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 7.5/10. Published 2025-12-05.

How severe is CVE-2025-66418?

High severity. CVSS v3 base score is 7.5 out of 10.

Resource exhaustion in Python Urllib3

CVE-2025-66418

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 comp…

EPSS: 0.006 (46.4th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

Affected products

Python Urllib3
Urllib3 — versions >= 1.24, < 2.6.0

Weakness classification (CWE)

CWE-770 — Allocation of Resources Without Limits or Throttling

References

security-advisories@github.com (x_refsource_CONFIRM, Vendor Advisory)
security-advisories@github.com (Patch, x_refsource_MISC)

Frequently asked questions

What is CVE-2025-66418?: CVE-2025-66418 is a high-severity vulnerability in Python Urllib3, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 7.5/10. Published 2025-12-05.
How severe is CVE-2025-66418?: High severity. CVSS v3 base score is 7.5 out of 10.