OpenSSH through 8.7 allows remote attackers, who have a suspicion that a certain combination of username and public key is known to an SSH server, to test whether this suspicion is correct. This occurs because a challenge is sent only when that combination could be valid for a login session. CREATE(Triage):(User=admin) CVE-2016-20012 (https://nvd.nist.gov/vuln/detail/CVE-2016-20012)
