LoFP LoFP / a host failing to authenticate with multiple valid users against a remote host is not a common behavior for legitimate systems. possible false positive scenarios include but are not limited to vulnerability scanners, remote administration tools, missconfigyred systems, etc.

Techniques

Sample rules

Windows Multiple Users Remotely Failed To Authenticate From Host

Description

The following analytic identifies a source host failing to authenticate against a remote host with 30 unique users. This behavior could represent an adversary performing a Password Spraying attack against an Active Directory environment 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 4625 documents each and every failed attempt to logon to the local computer. This event generates on domain controllers, member servers, and workstations. Logon Type 3 describes an remote authentication attempt. This logic can be used for real time security monitoring as well as threat hunting exercises. This detection will trigger on the host that is the target of the password spraying attack. This could be a domain controller as well as a member server or workstation. The analytics returned fields allow analysts to investigate the event further by providing fields like source process name, source account and attempted user accounts.

Detection logic

 `wineventlog_security` EventCode=4625 Logon_Type=3 IpAddress!="-" 
| bucket span=5m _time 
| stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as tried_accounts by _time, IpAddress, Computer 
| rename Computer as dest
| where unique_accounts > 30 
| `windows_multiple_users_remotely_failed_to_authenticate_from_host_filter`

Windows Unusual Count Of Users Remotely Failed To Auth From Host

Description

The following analytic identifies a source host failing to authenticate against a remote host with multiple users. This behavior could represent an adversary performing a Password Spraying attack against an Active Directory environment to obtain initial access or elevate privileges. Event 4625 documents each and every failed attempt to logon to the local computer. This event generates on domain controllers, member servers, and workstations. Logon Type 3 describes an remote authentication attempt. 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 trigger on the host that is the target of the password spraying attack. This could be a domain controller as well as a member server or workstation. The analytics returned fields allow analysts to investigate the event further by providing fields like source process name, source account and attempted user accounts.

Detection logic

 `wineventlog_security`  EventCode=4625 Logon_Type=3 IpAddress!="-" 
| bucket span=2m _time 
| stats dc(TargetUserName) AS unique_accounts values(TargetUserName) as tried_accounts by _time, IpAddress, Computer 
| eventstats avg(unique_accounts) as comp_avg , stdev(unique_accounts) as comp_std by IpAddress, 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_remotely_failed_to_auth_from_host_filter`