CVE-2025-66471

urllib3 is a user-friendly HTTP client library for Python. Starting in version 1.0 and prior to 2.6.0, the Streaming API improperly handles highly compressed data. urllib3's streaming API is designed for the efficient handling of large HTTP responses by reading the content in chunks, rather than loading the entire response body into memory at once. When streaming a compressed response, urllib3 can perform decoding or decompression based on the HTTP Content-Encoding header (e.g., gzip, deflate, br, or zstd). The library must read compressed data from the network and decompress it until the requested chunk size is met. Any resulting decompressed data that exceeds the requested amount is held in an internal buffer for the next read operation. The decompression logic could cause urllib3 to fully decode a small amount of highly compressed data in a single operation. This can result in excessive resource consumption (high CPU usage and massive memory allocation for the decompressed data.

CVSS v3 7.5 HIGH

7.5^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://github.com/urllib3/urllib3/commit/c19571de34c47de3a766541b041637ba5f716ed7	Patch
https://github.com/urllib3/urllib3/security/advisories/GHSA-2xpw-w6gg-jr37	Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:python:urllib3:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2025-12-05 17:16

Updated : 2025-12-10 16:10

NVD link : CVE-2025-66471

Mitre link : CVE-2025-66471

CVE.ORG link : CVE-2025-66471

JSON object : View

Products Affected

python

urllib3

CWE

CWE-409

Improper Handling of Highly Compressed Data (Data Amplification)

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