Logon Scripts

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Logon Scripts
Technique
ID T1037
Tactic Lateral Movement, Persistence
Platform Windows Server 2003, Windows Server 2008, Windows Server 2012, Windows XP, Windows 7, Windows 8, Windows Server 2003 R2, Windows Server 2008 R2, Windows Server 2012 R2, Windows Vista, Windows 8.1, Windows 10, MacOS, OS X
System Requirements Write access to system or domain logon scripts
Data Sources File monitoring, Process monitoring
CAPEC ID CAPEC-564

Windows

Windows allows logon scripts to be run whenever a specific user or group of users log into a system.1 The scripts can be used to perform administrative functions, which may often execute other programs or send information to an internal logging server.

If adversaries can access these scripts, they may insert additional code into the logon script to execute their tools when a user logs in. This code can allow them to maintain persistence on a single system, if it is a local script, or to move laterally within a network, if the script is stored on a central server and pushed to many systems. Depending on the access configuration of the logon scripts, either local credentials or an administrator account may be necessary.

Mac

Mac allows login and logoff hooks to be run as root whenever a specific user logs into or out of a system. A login hook tells Mac OS X to execute a certain script when a user logs in, but unlike startup items, a login hook executes as root2. There can only be one login hook at a time though. If adversaries can access these scripts, they can insert additional code to the script to execute their tools when a user logs in.

Examples

  • JHUHUGIT has registered a Windows shell script under the Registry key HKCU\Environment\UserInitMprLogonScript to establish persistence.3

Mitigation

Restrict write access to logon scripts to specific administrators. Prevent access to administrator accounts by mitigating Credential Access techniques and limiting account access and permissions of Valid Accounts.

Identify and block potentially malicious software that may be executed through logon script modification by using whitelisting4 tools like AppLocker56 that are capable of auditing and/or blocking unknown programs.

Detection

Monitor logon scripts for unusual access by abnormal users or at abnormal times. Look for files added or modified by unusual accounts outside of normal administration duties.