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CVE-2023-43804

HighPublished

Cookie HTTP header isn't stripped on cross-origin redirects

Published: Oct 4, 2023
Updated: Nov 3, 2025
Assigning CNA: GitHub_M
Evidence observed: Sep 20, 2026

Primary CVSS

8.1/ 10High

nvd · CVSS 3.1

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

EPSS probability estimate

1.2%

Low · next 30 days

Percentile: 66.5%
Model date: Sep 21, 2026

EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.

Summary

urllib3 is a user-friendly HTTP client library for Python. urllib3 doesn't treat the `Cookie` HTTP header special or provide any helpers for managing cookies over HTTP, that is the responsibility of the user. However, it is possible for a user to specify a `Cookie` header and unknowingly leak information via HTTP redirects to a different origin if that user doesn't disable redirects explicitly. This issue has been patched in urllib3 version 1.26.17 or 2.0.5.

Sources

CVE-2023-43804PoC
Containerized three-tier lab reproducing CVE-2023-43804 urllib3 cookie leak via cross-origin redirects, with exploit script and patch verification.

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