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Elastic Docs ›Elastic Security Solution [8.15] ›Detections and alerts ›Prebuilt rule reference

Masquerading Space After Filename

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Masquerading Space After Filename

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This rules identifies a process created from an executable with a space appended to the end of the filename. This may indicate an attempt to masquerade a malicious file as benign to gain user execution. When a space is added to the end of certain files, the OS will execute the file according to it’s true filetype instead of it’s extension. Adversaries can hide a program’s true filetype by changing the extension of the file. They can then add a space to the end of the name so that the OS automatically executes the file when it’s double-clicked.

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: Linux
  • OS: macOS
  • Use Case: Threat Detection
  • Tactic: Defense Evasion
  • Data Source: Elastic Defend

Version: 7

Rule authors:

  • Elastic

Rule license: Elastic License v2

Setup

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Setup

If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2, events will not define event.ingested and default fallback for EQL rules was not added until version 8.2. Hence for this rule to work effectively, users will need to add a custom ingest pipeline to populate event.ingested to @timestamp. For more details on adding a custom ingest pipeline refer - https://www.elastic.co/guide/en/fleet/current/data-streams-pipeline-tutorial.html

Rule query

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process where host.os.type:("linux","macos") and event.type == "start" and
process.executable regex~ """/[a-z0-9\s_\-\\./]+\s""" and not (
  process.name in ("ls", "find", "grep", "xkbcomp") or
  process.executable like ("/opt/nessus_agent/*", "/opt/gitlab/sv/gitlab-exporter/*", "/tmp/ansible-admin/*") or
  process.parent.args in (
    "./check_rubrik", "/usr/bin/check_mk_agent", "/etc/rubrik/start_stop_bootstrap.sh", "/etc/rubrik/start_stop_agent.sh"
  )
)

Framework: MITRE ATT&CKTM

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