CVE-2025-66418

⚠️ high

Summary

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.

CVSS Score

7.5

High

EPSS Score

0.0

Exploit Probability

Published Date

2025-12-05

First Seen: 2026-01-05

📊 Relative Risk Intelligence

This CVE is Moderate Risk - more severe than 69.0% of all 328,009 vulnerabilities in our database.

#101,817

Above average severity

Severity Percentile

🎯 CISA SSVC Assessment Updated: Dec 5, 2025

🔍 Exploitation Status

None

No known exploits

⚙️ Automatable

YES

Can be exploited automatically

💥 Technical Impact

Partial

Limited system impact

SSVC data provided by CISA

Last Modified 2025-12-10

Source NVD 🔗

CVSS Vector 3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS Vector 4.0

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CWE IDs (Weakness Types)

CWE-770

📦 Affected Products 1

Vendor	Product	Status	Affected Versions
python	urllib3	Affected	≥ 1.24 < 2.6.0

🔗 References 2

https://github.com/urllib3/urllib3/commit/24d7b67eac...

Patch

https://github.com/urllib3/urllib3/security/advisori...

Vendor Advisory

🔗 Related CVEs 6

CVE ID	Severity	CVSS	Summary	Published
CVE-2026-44431	🔶 medium	5.3	urllib3 is an HTTP client library for Python. From 1.23 to before 2.7.0, cross-origin redirects followed from the low-le...	2026-05-13
CVE-2026-44432	⚠️ high	7.5	urllib3 is an HTTP client library for Python. From 2.6.0 to before 2.7.0, urllib3 could decompress the whole response in...	2026-05-13
CVE-2026-21441	⚠️ high	7.5	urllib3 is an HTTP client library for Python. urllib3's streaming API is designed for the efficient handling of large HT...	2026-01-07
CVE-2025-66471	⚠️ high	7.5	urllib3 is a user-friendly HTTP client library for Python. Starting in version 1.0 and prior to 2.6.0, the Streaming API...	2025-12-05
CVE-2025-50181	🔶 medium	5.3	urllib3 is a user-friendly HTTP client library for Python. Prior to 2.5.0, it is possible to disable redirects for all r...	2025-06-19
CVE-2025-50182	🔶 medium	5.3	urllib3 is a user-friendly HTTP client library for Python. Starting in version 2.2.0 and prior to 2.5.0, urllib3 does no...	2025-06-19

These CVEs affect the same products