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9.2 Critical

CVE-2026-19445 A remote, unauthenticated TLS client can make a server crash or call through a freed pointer if its sni_callback assigns…

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.

Affected products and versions

Product Affected versions Fixed in
CPython 3.15 3.15.0a1 → < 3.15.0rc3 3.15.0rc3
CPython 3.14 3.14.0 → < 3.14.8 3.14.8
CPython 3.13 3.13.0 → < 3.13.16 3.13.16
CPython 3.12 3.12.0 → < 3.12.15 3.12.15
CPython 3.11 3.11.0 → < 3.11.17 3.11.17
CPython 3.10 earliest → < 3.10.22 3.10.22

References

Timeline

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