The remote web server is running an outdated instance of OpenSSL and that is affected by a buffer underflow vulnerability.
According to its banner, the version of OpenSSL on the remote host is 1.0.1 prior to 1.0.1o, or 1.0.2 prior to 1.0.2c. It is therefore affected by an underflow condition in the ASN.1 encoder that is triggered when attempting to encode the value zero represented as a negative integer. This may allow a remote attacker to corrupt memory and potentially execute arbitrary code.
Upgrade OpenSSL to version 1.0.1o or 1.0.2c