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.
https://mail.python.org/archives/list/[email protected]/thread/Y6IKNZ2VZUS2L6CLQICSFUEMCLT7OLTY/
https://github.com/python/cpython/pull/161570
https://github.com/python/cpython/issues/161569
https://github.com/python/cpython/commit/ac1d49f4fbb33941475c5aa3cb663ab39d64cb73
https://github.com/python/cpython/commit/8eb3d2c1c41ca7ce628554413981c1eb763a1494
https://github.com/python/cpython/commit/4e9d037f1cfc8e29efcb1f67bc668e06ff2b6643
Published: 2026-11-09
Updated: 2026-11-10
Base Score: 5
Vector: CVSS2#AV:N/AC:L/Au:N/C:N/I:P/A:N
Severity: Medium
Base Score: 7.5
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Severity: High
Base Score: 6.3
Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
Severity: Medium