CVE-2026-19445

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.

• How can I get the fixes?
• What do statuses mean?

Severity score breakdown

CVSS version: CVSS v4.0

References

• MITRE
• NVD
• Launchpad
• Debian

Other references

• https://www.cve.org/CVERecord?id=CVE-2026-19445
• https://github.com/python/cpython/issues/156293
• https://github.com/python/cpython/pull/158504
• https://github.com/python/cpython/commit/63fab143d94cafae71850831acfb52041ba44af7 (3.15 branch)
• https://github.com/python/cpython/commit/cd7e51e7d4563866fbaa1e2521ae69b45daf3698 (v3.14.8)
• https://github.com/python/cpython/commit/d8717ed01717a9641686e6e6f83f0ab8af235e2c (v3.13.16)
• https://github.com/python/cpython/pull/158523 (3.11)
• 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/b12968cefe69ca1dcb8606c832ff73ee7dbf4ba8
• https://github.com/python/cpython/commit/cd7e51e7d4563866fbaa1e2521ae69b45daf3698
• https://github.com/python/cpython/commit/d8717ed01717a9641686e6e6f83f0ab8af235e2c
• https://github.com/python/cpython/commit/ec44b5a3258cbda947d5e07242ee562ed05ef24b
• https://mail.python.org/archives/list/security-announce@python.org/thread/QMQIUQB6WGGC3MI7I3WKQXOYOBDSPPS3/
• http://www.openwall.com/lists/oss-security/2026/09/30/17