CVE-2025-66471

Aliases:GHSA-2xpw-w6gg-jr37
Advisory lineage Upstream: 0 Downstream: 68
Analyzed
Published: 05 Dec 2025, 16:06
Last modified:05 Dec 2025, 19:33

Vulnerability Summary

Overall Risk (default)
medium
36/100
CVSS Score
8.9 HIGH
v4.0 (cve.org)
EPSS Score
0.02% LOW
0% probability 0.00%
KEV
Not listed
Ransomware
No reports
Public exploits
None found
Dark Web
Not detected

Timeline

05 Dec 2025, 16:06
Published
Vulnerability first disclosed
05 Dec 2025, 19:33
Last Modified
Vulnerability information updated

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.

CVSS Metrics

  • v4.0•HIGH•Score: 8.9CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H
  • v4.0•HIGH•Score: 8.9CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
  • v3.1•HIGH•Score: 7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Trends

Current EPSS score: 0.02%• Percentile: 5%

Techniques & Countermeasures

  • CWE-409•Improper Handling of Highly Compressed Data (Data Amplification)

    The product does not handle or incorrectly handles a compressed input with a very high compression ratio that produces a large output.

Affected Systems

  • PyPI•urllib3

    ≥ 1.0, < 2.6.0

  • python•urllib3

    ≥ 1.0, < 2.6.0

  • urllib3•urllib3

    ≥ 1.0, < 2.6.0

References (4)