CVE-2025-66418

VendorpythonProducturllib3DiscoveredDec 5, 2025UpdatedSep 25, 2026

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.

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CVSS v3.1

7.5 HIGH

EPSS

0.68%

probability of exploitation in 30 days

CISA KEV

Not listed

no confirmed exploitation reported

News coverage

sources referencing this CVE

Related IOCs

seen in the same coverage

EPSS Trend

Aug 16, 2026 → Sep 1, 2026

▼ 0.01pp

0.69% → 0.68% over 2 tracked changes

CVSS v3.1 Detail

Attack VectorNETWORK

Attack ComplexityLOW

Privileges RequiredNONE

User InteractionNONE

ScopeUNCHANGED

ConfidentialityNONE

IntegrityNONE

AvailabilityHIGH

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

Connections

5 relationships

CWE-770

source

Timeline

disclosure → media coverage

Dec 5, 2025

Disclosure — published as a CVE record. · last revised by NVD Sep 25, 2026