CVE-2025-66418— urllib3 allows an unbounded number of links in the decompression chain
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 1.24版本至2.6.0之前版本存在安全漏洞，该漏洞源于解压链中的链接数量无限制，可能导致高CPU使用率和大量内存分配。
Possible ATT&CK Techniques 1 AI
T1496 · Resource Hijacking
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I. Basic Information for CVE-2025-66418
Vulnerability Information
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Vulnerability Title
urllib3 allows an unbounded number of links in the decompression chain
Source: CVE Program / CVE List V5
Vulnerability 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.
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
不加限制或调节的资源分配
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 1.24版本至2.6.0之前版本存在安全漏洞，该漏洞源于解压链中的链接数量无限制，可能导致高CPU使用率和大量内存分配。
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
II. Public POCs for CVE-2025-66418
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IV. Related Vulnerabilities
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Same vendor: urllib3
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CVE-2026-97689
urllib3: HTTPResponse.stream()/read_chunked() buffers an unb -
CVE-2026-97688
urllib3: Chunked Deflate streaming can enter an infinite loo -
CVE-2026-97687
urllib3: HTTPS proxy TLS configuration may be ignored or ove -
CVE-2026-44431
urllib3: Sensitive headers forwarded across origins in proxi -
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urllib3: Decompression-bomb safeguards bypassed in parts of
Same weakness: CWE-770
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V. Comments for CVE-2025-66418
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