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Elastic Docs ›Elastic Security Solution [8.9] ›Downloadable rule update v8.9.5

Screensaver Plist File Modified by Unexpected Process

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Screensaver Plist File Modified by Unexpected Process

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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 (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

  • Domain: Endpoint
  • OS: macOS
  • Use Case: Threat Detection
  • Tactic: Persistence
  • Data Source: Elastic Defend

Version: 104

Rule authors:

  • Elastic

Rule license: Elastic License v2

Investigation guide

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## Triage and analysis

- 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

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file where host.os.type == "macos" and event.type != "deletion" and
  file.name: "com.apple.screensaver.*.plist" and
   file.path : (
      "/Users/*/Library/Preferences/ByHost/*",
      "/Library/Managed Preferences/*",
      "/System/Library/Preferences/*"
      ) and
  (
    process.code_signature.trusted == false or
    process.code_signature.exists == false or

    /* common script interpreters and abused native macOS bins */
    process.name : (
      "curl",
      "mktemp",
      "tail",
      "funzip",
      "python*",
      "osascript",
      "perl"
      )
   ) 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

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