Sendmail security:/etc/aliases file

SendmailIs the most important mail transmission agent. We need to be cautious about Sendmail security. I will introduce the/etc/aliases file to you.

If not properly and strictly managed, the alias file is used to obtain privileges. For example, many release versions contain the "decode" alias in the alias file. This situation is getting fewer and fewer.

This aims to provide users with a convenient way to transmit binary files through mail. At the place where the email is sent, the user converts the binary file to the ASCII format with "uuencode" and delivers the result to the recipient's "decode" alias. The alias sends the mail message to the "/usr/bin/uuencode" program through an MPS queue. This program transfers the message from ASCII to the original binary file.

Delete the "decode" alias. Similarly, for all aliases used to execute programs that are not placed in the smrsh directory, you must carefully check them. They may be suspicious and should be deleted. To make your changes take effect, run:

[Root @ deep] #/usr/bin/newaliases

Edit the alias file (vi/etc/aliases) and delete the following lines:

# Basic system aliases -- these MUST be present.

MAILER-DAEMON: postmaster

Postmaster: root

# General redirections for pseudo do accounts.

Bin: root

Daemon: root

Games: root ?? Delete this row

Ingres: root ?? Delete this row

Nobody: root

System: root ?? Delete this row

Toor: root ?? Delete this row

Uucp: root ?? Delete this row

# Well-known aliases.

Manager: root ?? Delete this row

Dumper: root ?? Delete this row

Operator: root ?? Delete this row

# Trap decode to catch security attacks

Decode: root ?? Delete this row

# Person who shoshould get root's mail

# Root: marc

Finally, run the "/usr/bin/newaliases" program to make the change take effect.

Through this article, I believe you have learned another skill to enhance the security of Sendmail. I hope it will help you!

• Smrsh for Sendmail security
• How to Set a virtual domain in Sendmail
• Introduction to Sendmail
• Illustration: Sendmail Working Environment
• Learn more about installing the DNS + Sendmail service in Linux
• How to install the Sendmail server in Linux
• Linux Sendmail Configuration Guide