Compression DLL Loaded by Unusual Process

Elastic Stack Serverless Security

Identifies the image load of a compression DLL. Adversaries will often compress and encrypt data in preparation for exfiltration.

Rule type: eql

Rule indices:

• logs-endpoint.events.library-*

Severity: low

Risk score: 21

Runs every: 60m

Searches indices from: now-119m (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: None

Tags:

• Domain: Endpoint
• OS: Windows
• Use Case: Threat Detection
• Tactic: Collection
• Data Source: Elastic Defend
• Rule Type: BBR

Version: 3

Rule authors:

• Elastic

Rule license: Elastic License v2

library where host.os.type == "windows" and event.action == "load" and
  dll.name : ("System.IO.Compression.FileSystem.ni.dll", "System.IO.Compression.ni.dll") and
  not
  (
    (
      process.executable : (
        "?:\\Program Files\\*",
        "?:\\Program Files (x86)\\*",
        "?:\\Windows\\Microsoft.NET\\Framework*\\mscorsvw.exe",
        "?:\\Windows\\System32\\sdiagnhost.exe",
        "?:\\Windows\\System32\\inetsrv\\w3wp.exe",
        "?:\\Windows\\SysWOW64\\inetsrv\\w3wp.exe",
        "?:\\ProgramData\\Microsoft\\Windows Defender Advanced Threat Protection\\DataCollection\\*\\OpenHandleCollector.exe"
      ) and process.code_signature.trusted == true
    ) or
    (
      process.name : "NuGet.exe" and process.code_signature.trusted == true and user.id : ("S-1-5-18", "S-1-5-20")
    )
  )

Framework: MITRE ATT&CKTM

• Tactic:

  • Name: Collection
  • ID: TA0009
  • Reference URL: https://attack.mitre.org/tactics/TA0009/

• Technique:

  • Name: Archive Collected Data
  • ID: T1560
  • Reference URL: https://attack.mitre.org/techniques/T1560/