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.

CVSS 4.0

9.2CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N

EPSS

0.5% chance of exploitation in the next 30 days; higher than 44% of CVEs (scores of 2026-10-25)

CWE

CWE-416

Published

2026-09-30

Modified

2026-10-03

Record from

the NVD, synced 2026-10-19

References

• 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

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