Query: EDR alert: possible Disable or Modify Windows Event Log (T1685.001)
Matching passage: T1685.001 Disable or Modify Windows Event Log. Tactics: defense impairment. Description: Adversaries may disable or modify the Windows Event Log to limit data that can be leveraged for detections and audits. Windows Event Log records user and system activity such as login attempts and process creation.(Citation: EventLog_Core_Technologies) This data is used by security tools and analysts to generate detections. The EventLog service maintains event logs from various system components and applications. By default, the service automatically starts when a system powers on. An audit policy, maintained by the Local Security Policy (secpol.msc), defines which system events the EventLog service logs. Security audit policy settings can be changed by running secpol.msc, then navigating to `Security Settings\Local Policies\Audit Policy` for basic audit policy settings or `Security Settings\Advanced Audit Policy Configuration` for advanced audit policy settings.(Citation: Microsoft Audit Policy)(Citation: Microsoft Adv Security Settings) `auditpol.exe` may also be used to set audit policies.(Citation: Microsoft auditpol) Adversaries may target system-wide logging or just that of a particular application. For example, the Windows EventLog service may be disabled using the `Set-Service -Name EventLog -Status Stopped` or `sc config eventlog start=disabled` commands (followed by manually stopping the service using `Stop-Service -Name EventLog`). Additionally, the service may be disabled by modifying the "Start" value in `HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\EventLog` then restarting the system for the change to take effect.(Citation: Disable_Win_Event_Logging)(Citation: disable_win_evt_logging) There are several ways to disable the EventLog service via registry key modification. Without Administrator privileges, adversaries may modify the "Start" value in the key `HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\WMI\Autologger\EventLog-Security`, then reboot the system to disable the Security EventLog.(Citation: winser19_file_overwrite_bug_twitter) W
Near-miss passage: T1685.005 Clear Windows Event Logs. Tactics: defense impairment. Description: Adversaries may clear Windows Event Logs to hide the activity of an intrusion. Windows Event Logs are a record of a computer's alerts and notifications. There are three system-defined sources of events: System, Application, and Security, with five event types: Error, Warning, Information, Success Audit, and Failure Audit. With administrator privileges, the event logs can be cleared with the following utility commands: * `wevtutil cl system` * `wevtutil cl application` * `wevtutil cl security` These logs may also be cleared through other mechanisms, such as the event viewer GUI or [PowerShell](https://attack.mitre.org/techniques/T1059/001). For example, adversaries may use the PowerShell command `Remove-EventLog -LogName Security` to delete the Security EventLog and after reboot, disable future logging. Note: events may still be generated and logged in the .evtx file between the time the command is run and the reboot.(Citation: disable_win_evt_logging) Adversaries may also attempt to clear logs by directly deleting the stored log files within `C:\Windows\System32\winevt\logs\`.