LoFP / a source user failing attempting to authenticate multiple users on a host is not a common behavior for regular systems. some applications, however, may exhibit this behavior in which case sets of users hosts can be added to an allow list. possible false positive scenarios include systems where several users connect to like mail servers, identity providers, remote desktop services, citrix, etc.

Techniques

• T1110
• T1110.003

Sample rules

Windows Unusual Count Of Users Fail To Auth Wth ExplicitCredentials

• source: splunk
• technicques:
  • T1110.003
  • T1110

Description

The following analytic identifies a source user failing to authenticate with multiple users using explicit credentials on a host. It leverages Windows Event Code 4648 and calculates the standard deviation for each host, using the 3-sigma rule to detect anomalies. This behavior is significant as it may indicate a Password Spraying attack, where an adversary attempts to gain initial access or elevate privileges. If confirmed malicious, this activity could lead to unauthorized access, privilege escalation, or further compromise of the Active Directory environment.

Detection logic

`wineventlog_security` EventCode=4648 Caller_User_Name!=*$ Target_User_Name!=*$ 
| bucket span=5m _time 
| stats dc(Target_User_Name) AS unique_accounts values(Target_User_Name) as  user by _time, Computer, Caller_User_Name 
| eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std by Computer 
| eval upperBound=(comp_avg+comp_std*3) 
| eval isOutlier=if(unique_accounts > 10 and unique_accounts >= upperBound, 1, 0) 
| search isOutlier=1 
| `windows_unusual_count_of_users_fail_to_auth_wth_explicitcredentials_filter`

Windows Multiple Users Fail To Authenticate Wth ExplicitCredentials

• source: splunk
• technicques:
  • T1110.003
  • T1110

Description

The following analytic identifies a source user failing to authenticate with 30 unique users using explicit credentials on a host. It leverages Windows Event 4648, which is generated when a process attempts an account logon by explicitly specifying account credentials. This detection is significant as it may indicate a Password Spraying attack, where an adversary attempts to gain initial access or elevate privileges within an Active Directory environment. If confirmed malicious, this activity could lead to unauthorized access, privilege escalation, and potential compromise of sensitive information.

Detection logic

`wineventlog_security` EventCode=4648 Caller_User_Name!=*$ Target_User_Name!=*$ 
| bucket span=5m _time 
| stats dc(Target_User_Name) AS unique_accounts values(Target_User_Name) as  tried_account by _time, Computer, Caller_User_Name 
| where unique_accounts > 30 
| `windows_multiple_users_fail_to_authenticate_wth_explicitcredentials_filter`