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Screensaver Plist File Modified by Unexpected Process

Elastic Stack Serverless Security

Identifies when a screensaver plist file is modified by an unexpected process. An adversary can maintain persistence on a macOS endpoint by creating a malicious screensaver (.saver) file and configuring the screensaver plist file to execute code each time the screensaver is activated.

Rule type: eql

Rule indices:

  • auditbeat-*
  • logs-endpoint.events.*

Severity: medium

Risk score: 47

Runs every: 5m

Searches indices from: now-9m (https://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html#date-math[Date Math format], see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

  • Elastic
  • Host
  • macOS
  • Threat Detection
  • Persistence

Version: 4

Rule authors:

  • Elastic

Rule license: Elastic License v2

Investigation guide

  • Analyze the plist file modification event to identify whether the change was expected or not
  • Investigate the process that modified the plist file for malicious code or other suspicious behavior
  • Identify if any suspicious or known malicious screensaver (.saver) files were recently written to or modified on the host

Rule query

file where event.type != "deletion" and
  file.name: "com.apple.screensaver.*.plist" and
  file.path : (
    "/Users/*/Library/Preferences/ByHost/*",
    "/Library/Managed Preferences/*",
    "/System/Library/Preferences/*"
    ) and
  /* Filter OS processes modifying screensaver plist files */
  not process.executable : (
    "/usr/sbin/cfprefsd",
    "/usr/libexec/xpcproxy",
    "/System/Library/CoreServices/ManagedClient.app/Contents/Resources/MCXCompositor",
    "/System/Library/CoreServices/ManagedClient.app/Contents/MacOS/ManagedClient"
    )

Framework: MITRE ATT&CKTM