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CVE-2025-66418

7.5 · HIGH

urllib3 is a user-friendly HTTP client library for Python.

Published Dec 5, 2025CWE-770EPSS 0.68%

Overview

CVE-2025-66418 is a high-severity vulnerability. It was published on December 5, 2025 and has a CVSS 3.1 base score of 7.5 (HIGH).

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/urllib3/urllib3/commit/24d7b67eac89f94e11003424bcf0d8f7b72222a8GitHubgithub.com/urllib3/urllib3/security/advisories/GHSA-gm62-xv2j-4w53

How CyberStrike helps

Frequently asked questions

What is CVE-2025-66418?

CVE-2025-66418 is a high-severity vulnerability. It was published on December 5, 2025 and has a CVSS 3.1 base score of 7.5 (HIGH).

How severe is CVE-2025-66418?

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2025-66418?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2025-66418?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2025-66418 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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