High severity · published Dec 5, 2025
CVE-2025-66418
urllib3 is a user-friendly HTTP client library for Python
7.5
CVSS
0.7%
EPSS
No
On KEV
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
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.7% · higher than 52% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
UR
Urllib3 · Python
1.24 before 2.6.0 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-66418
CVE.org
https://www.cve.org/CVERecord?id=CVE-2025-66418
Patch
https://github.com/urllib3/urllib3/commit/24d7b67eac89f94e11003424bcf0d8f7b72222a8
Vendor Advisory
https://github.com/urllib3/urllib3/security/advisories/GHSA-gm62-xv2j-4w53
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