Server denial-of-service by using sslv2 message format in a HelloRetryRequest handshake

If a TLS1.3 enabled s2n-tls server receives an sslv2 ClientHello format message in a HelloRetryRequest handshake, the server may restart due to a NULL pointer dereference.

Applications using s2n are expected to restart following a NULL pointer dereference, and client applications may also retry requests. No AWS service was impacted by this issue and AWS customers do not need to take any action. s2n-tls users who enabled TLS1.3 in their applications should update to the most recent s2n-tls version.

All versions of s2n-tls from commit 397382111523a94f95cc551c4ca4d1eaf884ef35 through commit c947a221e1caadf12a262a6bf548f5f082e096be are affected by this issue.

Affected s2n-tls users should fetch s2n-tls commit 8cf81d3976dddb00b0050b0cfafcb41ea2a3bde5.