IMPORTANT: No additional bug fixes or documentation updates will be released for this version. For the latest information, see the current release documentation.

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PowerShell Suspicious Payload Encoded and Compressed

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PowerShell Suspicious Payload Encoded and Compressed

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Identifies the use of .NET functionality for decompression and base64 decoding combined in PowerShell scripts, which malware and security tools heavily use to deobfuscate payloads and load them directly in memory to bypass defenses.

Rule type: query

Rule indices:

winlogbeat-*
logs-windows.*

Severity: medium

Risk score: 47

Runs every: 5 minutes

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

Tags:

Elastic
Host
Windows
Threat Detection
Defense Evasion

Version: 3 (version history)

Added (Elastic Stack release): 8.0.0

Last modified (Elastic Stack release): 8.2.0

Rule authors: Elastic

Rule license: Elastic License v2

Potential false positives

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Legitimate PowerShell Scripts which makes use of compression and encoding.

Rule query

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event.category:process and powershell.file.script_block_text : (
( "System.IO.Compression.DeflateStream" or
"System.IO.Compression.GzipStream" or
"IO.Compression.DeflateStream" or "IO.Compression.GzipStream"
) and FromBase64String )

Threat mapping

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Framework: MITRE ATT&CK^TM

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/
Tactic:
- Name: Execution
- ID: TA0002
- Reference URL: https://attack.mitre.org/tactics/TA0002/
Technique:
- Name: Command and Scripting Interpreter
- ID: T1059
- Reference URL: https://attack.mitre.org/techniques/T1059/

Rule version history

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Version 3 (8.2.0 release)

Updated query, changed from:

event.category:process and powershell.file.script_block_text : (
(System.IO.Compression.DeflateStream or
System.IO.Compression.GzipStream or IO.Compression.DeflateStream or
IO.Compression.GzipStream) and FromBase64String )

Version 2 (8.1.0 release)

Formatting only

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