Mastering Linux Security and Hardening - Second Edition

Hands-on lab – disabling weak SSH encryption algorithms – Ubuntu 18.04

For this lab, you'll need the VM that you've been using as a scanner, and another Ubuntu 18.04 VM to scan and configure. Let's get started:

1. If you haven't done so already, scan the Ubuntu 18.04 VM and save the output to a file:

sudo ssh_scan -t 192.168.0.7 -o ssh_scan-7.json

2. On the target Ubuntu 18.04 VM, open the /etc/ssh/sshd_config file in your preferred text editor. Toward the top of the file, find these two lines:

# Ciphers and keying#RekeyLimit default none

3. Beneath those two lines, insert these three lines:

Ciphers -aes128-ctr,aes192-ctr,[e-mail] ecdh-sha2-nistp384MACs [e-mail],hmac-sha1,[e-mail],[e-mail],[e-mail],[e-mail],[e-mail],hmac-sha2-256 ...