Simple ball knowledge

defaultcreds-cheat-sheet

The defaultcreds-cheat-sheet pip package checks for default credentials.

#install 
pip3 install defaultcreds-cheat-sheet
# use 
creds search <service>
#eg,
creds search smb
creds search linksys

Linux stores previous passwords in /etc/security/opasswd

If you configure PAM to block reuse of old passwords, PAM stores those passwords in the /etc/security/opasswd file.