The issue is related to the use of defective cryptographic algorithms in the golang.org/x/crypto/ssh package, which can cause a crash in SSH servers under certain circumstances involving AddHostKey. An attacker can exploit this to crash a server. The vulnerability is triggered when a Signer is passed to ServerConfig.AddHostKey that does not implement AlgorithmSigner and returns a key of type “ssh-rsa” from its PublicKey method.