Information
The recommendation is to change the default sendmail greeting string to not display the sendmail version and other related information.
Rationale:
The sendmail deamon has a history of security vulnerabilities. The recommendation is to change the default sendmail greeting string so as not to display the sendmail version and other related information, which can be used by an attacker for fingerprinting purposes.
Solution
Create a backup copy of /etc/mail/sendmail.cf:
cp -p /etc/mail/sendmail.cf /etc/mail/sendmail.cf.pre_cis
Edit:
vi /etc/mail/sendmail.cf
Replace:
O SmtpGreetingMessage=$j Sendmail $b
With:
O SmtpGreetingMessage=mailerready
Default Value:
SmtpGreetingMessage=$j Sendmail $b
Additional Information:
Reversion:
Copy back the original /etc/sendmail.cf file:
cp -p /etc/mail/sendmail.cf.pre_cis /etc/mail/sendmail.cf