CVE-2026-84783 Use-After-Free in X.509 Extension Cache Under Concurrent Use

Issue summary: The first concurrent use of the same X.509 certificate by several threads may cause its cached extension data to be freed while another thread is still using it. Impact summary: A remote, unauthenticated peer could crash a multi-threaded TLS client, or a multi-threaded TLS server...

CVE-2026-84783

A use-after-free vulnerability exists in OpenSSL 4.0 due to improper synchronization during the two-phase caching of decoded X.509v3 certificate extensions. When multiple threads simultaneously decode and cache extensions for a shared trusted CA certificate , a thread may free the cached data whi...