Issue summary: In a server or client configuration with RFC7250 Raw Public Keys (RPKs)
enabled, and only the private key (with no associated certificate) configured locally,
a NULL pointer dereference may occur when the remote peer solicits raw public keys and
also sends the typically omitted "signature_algorithms_cert" TLS extension.

Impact summary: The impact is limited to a possible Denial of Service as a result of
an application abort, no data disclosure or remote command execution are possible.

CWE: CWE-476: NULL Pointer Dereference

Description: While a passing comment in sample code in the documentation suggests
that key-only RPK configurations are supported, the best-practice RPK configuration
is to always configure a corresponding certificate (possibly self-signed or
signed by any convenient CA).

When the private key is configured along with a matching certificate, the
"signature_algorithms_cert" extension is handled reliably even without the
fix, and peer clients or servers that don't support raw public keys may be
able to complete a TLS connection by pinning or verifying the corresponding
certificate or its public key.

Deployments that prefer to configure just a private key with no certificate
need to upgrade to an updated release as noted below.

FIPS impact: no

No FIPS modules are affected by this issue, as the SSL protocol implementation
is outside the OpenSSL FIPS module boundary.