Vulnerability in fetchmail 5.5.0-2 and earlier in the AUTHENTICATE GSSAPI command.
https://exchange.xforce.ibmcloud.com/vulnerabilities/7455
https://euvd.enisa.europa.eu/vulnerability/EUVD-2001-0101
http://www.turbolinux.com/pipermail/tl-security-announce/2000-December/000027.html