Detect Login Hook in Splunk
Adversaries may use a Login Hook to establish persistence executed upon user logon on macOS. A login hook is a plist file that points to a specific script to execute with root privileges upon user logon. The plist file is located at /Library/Preferences/com.apple.loginwindow.plist and can be modified using the defaults command-line utility. Login hooks (LoginHook key) and logout hooks (LogoutHook key) both require administrator permissions to modify. Adversaries insert a path to a malicious script into the plist, which executes upon the next user login. Only one login and one logout hook can exist on a system at a time. Note: Login hooks were deprecated in macOS 10.11 in favor of Launch Daemons and Launch Agents, but they continue to function on newer systems.
MITRE ATT&CK
- Tactic
- Persistence Privilege Escalation
- Sub-technique
- T1037.002 Login Hook
- Canonical reference
- https://attack.mitre.org/techniques/T1037/002/
SPL Detection Query
index=syslog OR index=mac_logs sourcetype="syslog" OR sourcetype="linux_secure" OR sourcetype="macos_secure"
| eval raw_lower = lower(_raw)
| where (match(raw_lower, "defaults") AND match(raw_lower, "com\.apple\.loginwindow"))
OR match(raw_lower, "loginhook")
OR match(raw_lower, "logouthook")
OR (match(raw_lower, "loginwindow\.plist") AND match(raw_lower, "(write|create|open|truncate)"))
| eval HookType = case(
match(raw_lower, "loginhook"), "LoginHook",
match(raw_lower, "logouthook"), "LogoutHook",
true(), "unknown"
)
| eval DefaultsWrite = if(match(raw_lower, "defaults.*write.*loginwindow"), 1, 0)
| eval PlistDirectWrite = if(match(raw_lower, "loginwindow\.plist") AND match(raw_lower, "(write|create|truncate|rename)"), 1, 0)
| eval ScriptPath = coalesce(
mvindex(split(rex(field=_raw, "(?i)(LoginHook|LogoutHook)\s+([/\w\-.]+)"), " "), 2),
"unknown"
)
| rex field=_raw "(?i)(?:defaults\s+write\s+[^\s]+\s+(?:Login|Logout)Hook\s+)(?<extracted_script>[/\w.\-]+)"
| eval SuspicionScore = DefaultsWrite + PlistDirectWrite
| where SuspicionScore > 0 OR HookType != "unknown"
| table _time, host, sourcetype, HookType, DefaultsWrite, PlistDirectWrite, extracted_script, SuspicionScore, _raw
| sort - _timeDetects macOS Login Hook persistence (T1037.002) using syslog data forwarded to Splunk. Monitors for the 'defaults write' command targeting com.apple.loginwindow with LoginHook or LogoutHook keys, direct plist file modifications, and any raw log entries referencing the LoginHook or LogoutHook strings. Extracts the hook type and the script path being registered. A suspicion score is calculated based on the number of matching indicators. Works with macOS syslog forwarded via syslog, syslog-ng, or Splunk Universal Forwarder.
Data Sources
Required Sourcetypes
False Positives & Tuning
- MDM solutions (Jamf Pro, Mosyle, Kandji) legitimately writing LoginHook entries as part of managed configuration profiles and onboarding workflows
- IT administrators manually configuring login scripts for legitimate enterprise purposes such as drive mapping or authentication setup
- Security software or compliance agents that use login hooks for startup checks on older macOS versions (pre-10.11)
- Migration scripts or imaging tools that configure loginwindow plist as part of macOS system setup or re-imaging processes
Other platforms for T1037.002
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Register Malicious Login Hook via defaults write
Expected signal: macOS Unified Log entries for the 'defaults' process with arguments 'write /Library/Preferences/com.apple.loginwindow LoginHook /tmp/argus_login_hook_test.sh'. File modification event for /Library/Preferences/com.apple.loginwindow.plist. Syslog entries showing the defaults command execution. EDR process telemetry showing parent shell spawning defaults binary with loginwindow plist arguments.
- Test 2Register Logout Hook via defaults write
Expected signal: macOS Unified Log entries showing defaults process execution with 'write', 'com.apple.loginwindow', and 'LogoutHook' arguments. File modification timestamp update on /Library/Preferences/com.apple.loginwindow.plist. Syslog entries capturing the command. EDR file write event for the plist file.
- Test 3Direct Plist Modification of loginwindow.plist via PlistBuddy
Expected signal: macOS Unified Log entries for PlistBuddy process (/usr/libexec/PlistBuddy) accessing /Library/Preferences/com.apple.loginwindow.plist. File write/modification event for the plist. EDR file modification telemetry showing PlistBuddy as the modifying process. Note: 'defaults' command will NOT appear in logs for this variant — detections must also cover direct plist modification.
- Test 4Read Existing Login Hook to Identify Persistence (Discovery Phase)
Expected signal: macOS Unified Log entries for 'defaults read' commands targeting com.apple.loginwindow. Multiple defaults process executions in rapid succession (read pattern vs. write pattern). If existing hook script was modified, file modification events for that script. Syslog entries showing defaults process activity.
References (9)
- https://attack.mitre.org/techniques/T1037/002/
- https://developer.apple.com/library/archive/documentation/MacOSX/Conceptual/BPSystemStartup/Chapters/CustomLogin.html
- https://developer.apple.com/documentation/devicemanagement/loginwindowscripts
- https://www.sentinelone.com/blog/how-malware-persists-on-macos/
- https://taomm.org/PDFs/vol1/CH%200x02%20Persistence.pdf
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1037.002/T1037.002.md
- https://objective-see.org/blog.html
- https://ss64.com/osx/defaults.html
- https://support.apple.com/en-us/HT203539
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