CVE-2026-124249
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CookieJar Deletes Cookies via Expired Set-Cookie Header

Publication date: 2026-11-09

Last updated on: 2026-11-09

Assigner: Python Software Foundation

Description
http.cookiejar.CookieJar deleted a stored cookie when a response carried an already expired Set-Cookie header for it, using the Domain and Path attributes from the header without consulting the cookie policy. A server could therefore delete cookies belonging to other domains from a shared cookie jar, such as the one used by urllib's HTTPCookieProcessor. The fix consults the cookie policy before an expired cookie may delete an existing one, as required by RFC 6265 section 5.3.

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Meta Information

Published
2026-11-09
Last Modified
2026-11-09
Generated
2026-11-09
AI Q&A
2026-11-09
EPSS Evaluated
N/A
NVD
CVE-2026-124249
EUVD
EUVD-2026-120068

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
python cookiejar *

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-346 The product does not properly verify that the source of data or communication is valid.

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Executive Summary

CVE-2026-124249 is a vulnerability in Python's http.cookiejar.CookieJar where an expired Set-Cookie header could delete stored cookies for other domains without checking the cookie policy first. This violates RFC 6265 section 5.3, which requires domain checks before removing cookies. A malicious server could exploit this to delete cookies belonging to different domains in a shared cookie jar.

Impact Analysis

This vulnerability could allow an attacker to delete cookies for other domains in a shared cookie jar. This might disrupt user sessions, log users out of applications, or enable session hijacking if cookies are improperly managed. It primarily affects applications using urllib's HTTPCookieProcessor with shared cookie storage.

Mitigation Strategies
  • Update Python to a patched version where the fix for CVE-2026-124249 has been applied, specifically versions 3.11 through 3.16.
  • Review applications using http.cookiejar.CookieJar or urllib's HTTPCookieProcessor to ensure they are using the updated Python versions.
  • Monitor cookie jar behavior in shared environments to detect unexpected cookie deletions across domains.

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