Brute Force: Password Spraying
Adversaries may use a single or small list of commonly used passwords against many different accounts to attempt to acquire valid account credentials. Password spraying uses one password (e.g. 'Password01'), or a small list of commonly used passwords, that may match the complexity policy of the domain. Logins are attempted with that password against many different accounts on a network to avoid account lockouts that would normally occur when brute forcing a single account with many passwords. 
Typically, management services over commonly used ports are used when password spraying. 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.
In default environments, LDAP and Kerberos connection attempts are less likely to trigger events over SMB, which creates Windows "logon failure" event ID 4625.
APT28 has used a brute-force/password-spray tooling that operated in two modes: in password-spraying mode it conducted approximately four authentication attempts per hour per targeted account over the course of several days or weeks.
Lazarus Group malware attempts to connect to Windows shares for lateral movement by using a generated list of usernames, which center around permutations of the username Administrator, and weak passwords.
|Account Use Policies||
Set account lockout policies after a certain number of failed login attempts to prevent passwords from being guessed. Too strict a policy may create a denial of service condition and render environments un-usable, with all accounts used in the brute force being locked-out.
Use multi-factor authentication. Where possible, also enable multi-factor authentication on externally facing services.
Refer to NIST guidelines when creating password policies. 
Monitor authentication logs for system and application login failures of Valid Accounts. Specifically, monitor for many failed authentication attempts across various accounts that may result from password spraying attempts.
Consider the following event IDs:
- Domain Controllers: "Audit Logon" (Success & Failure) for event ID 4625.
- Domain Controllers: "Audit Kerberos Authentication Service" (Success & Failure) for event ID 4771.
- All systems: "Audit Logon" (Success & Failure) for event ID 4648.
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