Compression DLL Loaded by Unusual Process

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 (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

Rule query

edit

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&CK^TM

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/

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