Credential Stuffing

Adversaries may use credentials obtained from breach dumps of unrelated accounts to gain access to target accounts through credential overlap. Occasionally, large numbers of username and password pairs are dumped online when a website or service is compromised and the user account credentials accessed. The information may be useful to an adversary attempting to compromise accounts by taking advantage of tendency for users to use the same passwords across personal and business accounts.
Credential stuffing is a risky option because it could cause numerous authentication failures and account lockouts, depending on the organization's login failure policies.
Typically, management services over commonly used ports are used when stuffing credentials. Commonly targeted services include the following:
· SSH (22/TCP)
· Telnet (23/TCP)
· FTP (21/TCP)
· NetBIOS / SMB / Samba (139/TCP & 445/TCP)
· LDAP (389/TCP)
· Kerberos (88/TCP)
· RDP / Terminal Services (3389/TCP)
· HTTP/HTTP Management Services (80/TCP & 443/TCP)
· MSSQL (1433/TCP)
· Oracle (1521/TCP)
· MySQL (3306/TCP)
· VNC (5900/TCP)
In addition to management services, adversaries may "target single sign-on (SSO) and cloud-based applications utilizing federated authentication protocols," as well as externally facing email applications, such as Office 365.[​
The procedure for this technique is usually gaining the stolen credentials for this attack. Even though it is very simple to Buy and Find I will not point to any resources that will help in this attack(Let's be honest a simple Google Search is enough). But once the DB of Credentials are found you might get lucky and actually login to the service they are meant for since large scale organizations have the tendency of reusing these logins.