CVE-2026-21441 (High) detected in urllib3-2.6.2-py3-none-any.whl - autoclosed

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CVE-2026-21441 - High Severity Vulnerability

Vulnerable Library - urllib3-2.6.2-py3-none-any.whl

HTTP library with thread-safe connection pooling, file post, and more.

Library home page: https://files.pythonhosted.org/packages/6d/b9/4095b668ea3678bf6a0af005527f39de12fb026516fb3df17495a733b7f8/urllib3-2.6.2-py3-none-any.whl

Path to dependency file: /dev-requirements.txt

Path to vulnerable library: /tmp/ws-ua_20251216051935_TCQRRN/python_AMRZXA/202512160520121/env/lib/python3.9/site-packages/urllib3-2.6.2.dist-info,/tmp/ws-ua_20251216051935_TCQRRN/python_AMRZXA/202512160520121/env/lib/python3.9/site-packages/urllib3-2.6.2.dist-info,/tmp/ws-ua_20251216051935_TCQRRN/python_AMRZXA/202512160520121/env/lib/python3.9/site-packages/urllib3-2.6.2.dist-info,/tmp/ws-ua_20251216051935_TCQRRN/python_AMRZXA/202512160520121/env/lib/python3.9/site-packages/urllib3-2.6.2.dist-info,/tmp/ws-ua_20251216051935_TCQRRN/python_AMRZXA/202512160520121/env/lib/python3.9/site-packages/urllib3-2.6.2.dist-info

Dependency Hierarchy:

• ❌ urllib3-2.6.2-py3-none-any.whl (Vulnerable Library)

Found in HEAD commit: 1219877a9048ae8b9aafb22346da2f2c780c3cf2

Found in base branch: 2.2

Vulnerability Details

urllib3 is an HTTP client library for Python. 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. urllib3 can perform decoding or decompression based on the HTTP "Content-Encoding" header (e.g., "gzip", "deflate", "br", or "zstd"). When using the streaming API, the library decompresses only the necessary bytes, enabling partial content consumption. Starting in version 1.22 and prior to version 2.6.3, for HTTP redirect responses, the library would read the entire response body to drain the connection and decompress the content unnecessarily. This decompression occurred even before any read methods were called, and configured read limits did not restrict the amount of decompressed data. As a result, there was no safeguard against decompression bombs. A malicious server could exploit this to trigger excessive resource consumption on the client. Applications and libraries are affected when they stream content from untrusted sources by setting "preload_content=False" when they do not disable redirects. Users should upgrade to at least urllib3 v2.6.3, in which the library does not decode content of redirect responses when "preload_content=False". If upgrading is not immediately possible, disable redirects by setting "redirect=False" for requests to untrusted source.

Publish Date: 2026-01-07

URL: CVE-2026-21441

CVSS 3 Score Details (8.6)

Base Score Metrics:

• Exploitability Metrics:
  • Attack Vector: Network
  • Attack Complexity: Low
  • Privileges Required: None
  • User Interaction: None
  • Scope: Changed
• Impact Metrics:
  • Confidentiality Impact: None
  • Integrity Impact: None
  • Availability Impact: High

For more information on CVSS3 Scores, click here.

Suggested Fix

Type: Upgrade version

Origin: GHSA-38jv-5279-wg99

Release Date: 2026-01-07

Fix Resolution: 2.6.3

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• Check this box to open an automated fix PR

[mend-for-github-com]

✔️ This issue was automatically closed by Mend because the vulnerable library in the specific branch(es) was either marked as ignored or it is no longer part of the Mend inventory.