Description
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.
References
- www.cve.org/CVERecord ↗
- nvd.nist.gov/vuln/detail/CVE-2026-19445 ↗
- github.com/python/cpython/commit/34a53dce8174da2fceb12fe084a4def02a10053d ↗
- github.com/python/cpython/commit/46133cd57d309652139ada74014aca7665ac552b ↗
- github.com/python/cpython/commit/63fab143d94cafae71850831acfb52041ba44af7 ↗
- github.com/python/cpython/commit/b12968cefe69ca1dcb8606c832ff73ee7dbf4ba8 ↗
- github.com/python/cpython/commit/cd7e51e7d4563866fbaa1e2521ae69b45daf3698 ↗
- github.com/python/cpython/commit/d8717ed01717a9641686e6e6f83f0ab8af235e2c ↗
- github.com/python/cpython/commit/ec44b5a3258cbda947d5e07242ee562ed05ef24b ↗
- github.com/python/cpython/issues/156293 ↗
- github.com/python/cpython/pull/158504 ↗
- mail.python.org/archives/list/security-announce@python.org/thread/QMQIUQB6WGGC3MI7I3WKQXOYOBDSPPS3/ ↗
- www.openwall.com/lists/oss-security/2026/09/30/17 ↗
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This product uses the NVD API but is not endorsed or certified by the NVD. CVSS scores do not establish exploitation.