The remote Debian host is missing a security-related update.
Michael Eder and Thomas Kittel discovered that Heimdal, an implementation of Kerberos 5 that aims to be compatible with MIT Kerberos, did not correctly handle ASN.1 data. This would allow an unauthenticated remote attacker to cause a denial of service (crash of the KDC daemon) by sending maliciously crafted packets.
Upgrade the heimdal packages. For the stable distribution (stretch), this problem has been fixed in version 7.1.0+dfsg-13+deb9u2.