CVE-2026-19445: Python Software Foundation Cpython

Critical severity, CVSS 9.2. EPSS: 0.4% chance of exploitation in the next 30 days.

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.

Affected products

• Python Software Foundation Cpython: before 3.10.22 (fixed in 3.10.22); from 3.11.0, before 3.11.17 (fixed in 3.11.17); from 3.12.0, before 3.12.15 (fixed in 3.12.15); from 3.13.0, before 3.13.16 (fixed in 3.13.16); from 3.14.0, before 3.14.8 (fixed in 3.14.8); from 3.15.0a1, before 3.15.0rc3 (fixed in 3.15.0rc3)

Published 2026-09-30. Last modified 2026-10-03.