CVE-2026-19445 — Use-after-free of a server-side SSLContext when sni_callback switches contexts
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…
Published: 2026-09-30 · CVSS: 9.2 · CVSS 4.0
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.
Source: CVE Program · Revision 8b16575c39f1e1810c5e863010da073d2d3285e7