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CVE-2025-66418

urllib3 allows an unbounded number of links in the decompression chain

Published: Dec 5, 2025Updated: Dec 10, 2025 Sources: CVE List NVD GHSA BDUCWE-770
NVD MITRE
7.5CVSSHIGH
EPSS Score
0.5%
Top 59.3%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

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.

CVSS Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:NI:NA:H
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:NConfidentiality
None
I:NIntegrity
None
A:HAvailability
High
Open in CVSS calculator →

Weaknesses

CWE-770

Affected Products

urllib3urllib3
Library
OSS Libraries / pypi
urllib3PyPIOSS Libraries
Red Hat Enterprise LinuxRed Hat Inc.
On-premOS
Operating Systems / linux-distro
OpenShift Container PlatformRed Hat Inc.
SaaSSaaS Service
Cloud & SaaS / container-orchestration
UbuntuCanonical Ltd.
On-premOS
Operating Systems / linux-distro
urllib3oss-projectOSS Librariesaka urllib3
pypipackage-ecosystemOSS Libraries
red hat inc.commercialUSOperating Systemsaka red hat
canonical ltd.commercialGBOperating Systemsaka canonical
and 46 more affected products View all →

Attack Graph

Products CVE Techniques Tactics

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Exploitability

Official Patch Available

MITRE ATT&CK

1 technique
Impact
View detailed technique mapping

References

https://github.com/urllib3/urllib3/security/advisories/GHSA-gm62-xv2j-4w53
github.com
https://github.com/urllib3/urllib3/commit/24d7b67eac89f94e11003424bcf0d8f7b72222a8
github.com
https://nvd.nist.gov/vuln/detail/CVE-2025-66418
nvd.nist.gov
and 13 more references View all →

Timeline

Published
Dec 5, 2025
Last Updated
Dec 10, 2025

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