LoFP / a host failing to authenticate with multiple valid domain users is not a common behavior for legitimate systems. possible false positive scenarios include but are not limited to vulnerability scanners and missconfigured systems. if this detection triggers on a host other than a domain controller, the behavior could represent a password spraying attack against the host's local accounts.

• T1110
• T1110.003

Sample rules

Windows Unusual Count Of Users Failed To Authenticate Using NTLM

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

Description

The following analytic identifies one source endpoint failing to authenticate with multiple valid users using the NTLM protocol. This behavior could represent an adversary performing a Password Spraying attack against an Active Directory environment using NTLM to obtain initial access or elevate privileges. Event 4776 is generated on the computer that is authoritative for the provided credentials. For domain accounts, the domain controller is authoritative. For local accounts, the local computer is authoritative. Error code 0xC000006A means: misspelled or bad password (the attempted user is a legitimate domain user). The detection calculates the standard deviation for each host and leverages the 3-sigma statistical rule to identify an unusual number of users. To customize this analytic, users can try different combinations of the bucket span time and the calculation of the upperBound field. This logic can be used for real time security monitoring as well as threat hunting exercises. This detection will only trigger on domain controllers, not on member servers or workstations. The analytics returned fields allow analysts to investigate the event further by providing fields like source workstation name and attempted user accounts.

Detection logic

 `wineventlog_security`  EventCode=4776 TargetUserName!=*$ Status=0xC000006A 
| bucket span=2m _time 
| stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as tried_accounts by _time, Workstation 
| eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std by Workstation 
| 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_failed_to_authenticate_using_ntlm_filter`

Windows Multiple Users Failed To Authenticate From Host Using NTLM

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

Description

The following analytic identifies one source endpoint failing to authenticate with 30 unique valid users using the NTLM protocol. This behavior could represent an adversary performing a Password Spraying attack against an Active Directory environment using NTLM to obtain initial access or elevate privileges. Active Directory environments can be very different depending on the organization. Users should test this detection and customize the arbitrary threshold when needed. Event 4776 is generated on the computer that is authoritative for the provided credentials. For domain accounts, the domain controller is authoritative. For local accounts, the local computer is authoritative. Error code 0xC000006A means: misspelled or bad password (the attempted user is a legitimate domain user). This logic can be used for real time security monitoring as well as threat hunting exercises. This detection will only trigger on domain controllers, not on member servers or workstations. The analytics returned fields allow analysts to investigate the event further by providing fields like source workstation name and attempted user accounts.

Detection logic

 `wineventlog_security` EventCode=4776 TargetUserName!=*$ Status=0xC000006A 
| bucket span=5m _time 
| stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as tried_accounts by _time, Workstation 
| where unique_accounts > 30 
| `windows_multiple_users_failed_to_authenticate_from_host_using_ntlm_filter`

Windows Multiple Users Failed To Authenticate Using Kerberos

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

Description

The following analytic identifies one source endpoint failing to authenticate with 30 unique users using the Kerberos protocol. This behavior could represent an adversary performing a Password Spraying attack against an Active Directory environment using Kerberos to obtain initial access or elevate privileges. Active Directory environments can be very different depending on the organization. Users should test this detection and customize the arbitrary threshold when needed. Event 4771 is generated when the Key Distribution Center fails to issue a Kerberos Ticket Granting Ticket (TGT). Failure code 0x18 stands for wrong password provided (the attempted user is a legitimate domain user). This logic can be used for real time security monitoring as well as threat hunting exercises. This detection will only trigger on domain controllers, not on member servers or workstations. The analytics returned fields allow analysts to investigate the event further by providing fields like source ip and attempted user accounts.

Detection logic

`wineventlog_security` EventCode=4771 TargetUserName!="*$" Status=0x18 
| bucket span=5m _time 
| stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as user by _time, IpAddress 
| where unique_accounts > 30 
| `windows_multiple_users_failed_to_authenticate_using_kerberos_filter`

Windows Unusual Count Of Users Failed To Auth Using Kerberos

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

Description

The following analytic identifies one source endpoint failing to authenticate with multiple valid users using the Kerberos protocol. This behavior could represent an adversary performing a Password Spraying attack against an Active Directory environment using Kerberos to obtain initial access or elevate privileges. Event 4771 is generated when the Key Distribution Center fails to issue a Kerberos Ticket Granting Ticket (TGT). Failure code 0x18 stands for wrong password provided (the attempted user is a legitimate domain user). The detection calculates the standard deviation for each host and leverages the 3-sigma statistical rule to identify an unusual number of users. To customize this analytic, users can try different combinations of the bucket span time and the calculation of the upperBound field. This logic can be used for real time security monitoring as well as threat hunting exercises. This detection will only trigger on domain controllers, not on member servers or workstations. The analytics returned fields allow analysts to investigate the event further by providing fields like source ip and attempted user accounts.

Detection logic

`wineventlog_security` EventCode=4771 TargetUserName!="*$" Status=0x18 
| bucket span=5m _time 
| stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as user by _time, IpAddress 
| eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std by IpAddress 
| 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_failed_to_auth_using_kerberos_filter`