CVE-2026-19445
A remote, unauthenticated TLS client can make a server crash or call
through a freed pointer if its sni_callback assigns a different context to
SSLSocket.context (the documented way to select a certificate per server
name) and nothing else keeps the original ssl.SSLContext alive. Typical
cases are servers that create an SSLContext per connection or replace it
while connections are open; servers that wrap their listening socket with
it are not affected.
Mitigation: keep a reference to every SSLContext that sets sni_callback for
the lifetime of the server. TLS clients are not affected.
Package Versions Affected
Automatically patch vulnerabilities without upgrading
CVSS Version
Related Resources
References
https://github.com/python/cpython/pull/158504, https://mail.python.org/archives/list/security-announce@python.org/thread/QMQIUQB6WGGC3MI7I3WKQXOYOBDSPPS3/, https://github.com/python/cpython/issues/156293, https://github.com/python/cpython/commit/34a53dce8174da2fceb12fe084a4def02a10053d, https://github.com/python/cpython/commit/46133cd57d309652139ada74014aca7665ac552b, https://github.com/python/cpython/commit/63fab143d94cafae71850831acfb52041ba44af7, https://github.com/python/cpython/commit/cd7e51e7d4563866fbaa1e2521ae69b45daf3698, https://github.com/python/cpython/commit/d8717ed01717a9641686e6e6f83f0ab8af235e2c, https://github.com/python/cpython/commit/b12968cefe69ca1dcb8606c832ff73ee7dbf4ba8, https://github.com/python/cpython/commit/ec44b5a3258cbda947d5e07242ee562ed05ef24b