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CVE-2025-66471— urllib3 Streaming API improperly handles highly compressed data

Quick assessment

Affected
urllib3 urllib3
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

urllib3是urllib3开源的一款Python HTTP库。该产品具有线程安全连接池、文件发布支持等。 urllib3 1.0版本至2.6.0之前版本存在安全漏洞，该漏洞源于Streaming API处理高度压缩数据不当，可能导致资源消耗过高。

AI Predicted 7.5 Difficulty: Easy EPSS 0.68% · P52

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking
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I. Basic Information for CVE-2025-66471

Vulnerability Information
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Vulnerability Title
urllib3 Streaming API improperly handles highly compressed data
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
对高度压缩数据的处理不恰当(数据放大攻击)
Source: CVE Program / CVE List V5
Vulnerability Title
urllib3 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
urllib3是urllib3开源的一款Python HTTP库。该产品具有线程安全连接池、文件发布支持等。 urllib3 1.0版本至2.6.0之前版本存在安全漏洞，该漏洞源于Streaming API处理高度压缩数据不当，可能导致资源消耗过高。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
urllib3 urllib3 >= 1.0, < 2.6.0 -

II. Public POCs for CVE-2025-66471

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III. Intelligence Information for CVE-2025-66471

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IV. Related Vulnerabilities

Same product: urllib3
Same vendor: urllib3
Same weakness: CWE-409

V. Comments for CVE-2025-66471

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