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. [1]

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.[2]

In default environments, LDAP and Kerberos connection attempts are less likely to trigger events over SMB, which creates Windows "logon failure" event ID 4625.

ID: T1110.003
Sub-technique of:  T1110
Tactic: Credential Access
Platforms: AWS, Azure, Azure AD, GCP, Linux, Office 365, SaaS, Windows, macOS
Permissions Required: User
Data Sources: Authentication logs, Office 365 account logs
Contributors: John Strand; Microsoft Threat Intelligence Center (MSTIC)
Version: 1.0
Created: 11 February 2020
Last Modified: 29 March 2020

Procedure Examples

Name Description
APT33

APT33 has used password spraying to gain access to target systems.[9][10]

Lazarus Group

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.[7][8]

Leafminer

Leafminer used a tool called Total SMB BruteForcer to perform internal password spraying.[6]

Linux Rabbit

Linux Rabbit brute forces SSH passwords in order to attempt to gain access and install its malware onto the server. [5]

MailSniper

MailSniper can be used for password spraying against Exchange and Office 365.[4]

Mitigations

Mitigation Description
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.

Multi-factor Authentication

Use multi-factor authentication. Where possible, also enable multi-factor authentication on externally facing services.

Password Policies

Refer to NIST guidelines when creating password policies. [3]

Detection

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:[11]

  • 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.

References