Telnet is on by default in Solaris 10 and 11 and you may not even know it. Most security experts long have recommended against using telnet. There’s really no good reason to use telnet, nor is it safe. SANS analysts today reiterated their recommendation to cut out telnet in their diary entry about the new bug. Solaris users should care, and act fast, says SANS Internet Storm Center’s Bojan Zdrnja of the SANS Web Storm Center.”]
Source: https://www.darkreading.com/attacks-breaches/don-t-ask-don-t-telnet