Amazon Linux AMI Security Advisory: ALAS-2016-683
Advisory Release Date: 2016-04-06 14:40 Pacific
A type confusion issue was found in the way libssh2 generated ephemeral secrets for the diffie-hellman-group1 and diffie-hellman-group14 key exchange methods. This would cause an SSHv2 Diffie-Hellman handshake to use significantly less secure random parameters.
Run yum update libssh2 to update your system.