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.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
High
Difficult to exploit
Attack Requirements
Present
Additional conditions required
Privileges Required
None
No privileges needed
User Interaction
None
No user interaction needed
Impact Assessment
Confidentiality
High
Complete data leak
Integrity
High
Complete data modification
Availability
Low
Partial disruption
CVSS Vector v4.0
Weakness Type (CWE)
Vulnerable Products
python software foundation:cpython
References 11
https://github.com/python/cpython/issues/156293
cna@python.org
https://github.com/python/cpython/pull/158504
cna@python.org
https://mail.python.org/archives/list/security-announce@python.org/thread/QMQIU…
cna@python.org
http://www.openwall.com/lists/oss-security/2026/09/30/17
af854a3a-2127-422b-91ae-364da2661108
https://github.com/python/cpython/commit/34a53dce8174da2fceb12fe084a4def02a1005…
cna@python.org
https://github.com/python/cpython/commit/46133cd57d309652139ada74014aca7665ac55…
cna@python.org
https://github.com/python/cpython/commit/63fab143d94cafae71850831acfb52041ba44a…
cna@python.org
https://github.com/python/cpython/commit/cd7e51e7d4563866fbaa1e2521ae69b45daf36…
cna@python.org
https://github.com/python/cpython/commit/d8717ed01717a9641686e6e6f83f0ab8af235e…
cna@python.org
https://github.com/python/cpython/commit/b12968cefe69ca1dcb8606c832ff73ee7dbf4b…
NVD
https://github.com/python/cpython/commit/ec44b5a3258cbda947d5e07242ee562ed05ef2…
NVD