PowerShell Script with Encryption/Decryption Capabilities

Elastic Stack Serverless Security

Identifies the use of Cmdlets and methods related to encryption/decryption of files in PowerShell scripts, which malware and offensive security tools can abuse to encrypt data or decrypt payloads to bypass security solutions.

Rule type: query

Rule indices:

• winlogbeat-*
• logs-windows.*

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: None

Tags:

• Elastic
• Host
• Windows
• Threat Detection
• Defense Evasion
• PowerShell

Version: 1

Rule authors:

• Elastic

Rule license: Elastic License v2

event.category:process and
  powershell.file.script_block_text : (
    (
      "Cryptography.AESManaged" or
      "Cryptography.RijndaelManaged" or
      "Cryptography.SHA1Managed" or
      "Cryptography.SHA256Managed" or
      "Cryptography.SHA384Managed" or
      "Cryptography.SHA512Managed" or
      "Cryptography.SymmetricAlgorithm" or
      "PasswordDeriveBytes" or
      "Rfc2898DeriveBytes"
    ) and
    (
      CipherMode and PaddingMode
    ) and
    (
      ".CreateEncryptor" or
      ".CreateDecryptor"
    )
  ) and not user.id : "S-1-5-18"

Framework: MITRE ATT&CKTM

• Tactic:

  • Name: Defense Evasion
  • ID: TA0005
  • Reference URL: https://attack.mitre.org/tactics/TA0005/

• Technique:

  • Name: Deobfuscate/Decode Files or Information
  • ID: T1140
  • Reference URL: https://attack.mitre.org/techniques/T1140/

• Technique:

  • Name: Obfuscated Files or Information
  • ID: T1027
  • Reference URL: https://attack.mitre.org/techniques/T1027/