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Suspicious Portable Executable Encoded in Powershell Script

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Suspicious Portable Executable Encoded in Powershell Script

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Detects the presence of portable executables (PE) in a PowerShell script by looking for its encoded header. Attackers embed PEs into PowerShell scripts for injecting them into the memory, avoiding defenses by not writing to disk.

Rule type: query

Rule indices:

winlogbeat-*
logs-windows.*

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:

https://github.com/atc-project/atc-data/blob/master/docs/Logging_Policies/LP_0109_windows_powershell_script_block_log.md

Tags:

Elastic
Host
Windows
Threat Detection
Execution

Version: 4

Rule authors:

Elastic

Rule license: Elastic License v2

Investigation guide

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## Triage and analysis.

### Investigating Suspicious Portable Executable Encoded in Powershell Script

PowerShell is one of the main tools used by system administrators for automation, report routines, and other tasks.

Attackers can abuse PowerShell in-memory capabilities to inject executables into memory without touching the disk,
bypassing antivirus software. These executables are generally base64 encoded.

#### Possible investigation steps:

- Examine script content that triggered the detection.
- Investigate script execution chain (parent process tree).
- Inspect any file or network events from the suspicious PowerShell host process instance.
- If the action is suspicious for the user, check for any other activities done by the user in the last 48 hours.

### False Positive Analysis

- Verify whether the script content is malicious/harmful.

### Related Rules

- PowerShell Reflection Assembly Load - e26f042e-c590-4e82-8e05-41e81bd822ad
- PowerShell Suspicious Payload Encoded and Compressed - 81fe9dc6-a2d7-4192-a2d8-eed98afc766a
- PowerShell PSReflect Script - 56f2e9b5-4803-4e44-a0a4-a52dc79d57fe

### Response and Remediation

- Immediate response should be taken to validate, investigate, and potentially contain the activity to prevent further
post-compromise behavior.

## Config

The 'PowerShell Script Block Logging' logging policy must be enabled.
Steps to implement the logging policy with with Advanced Audit Configuration:

```
Computer Configuration >
Administrative Templates >
Windows PowerShell >
Turn on PowerShell Script Block Logging (Enable)
```

Steps to implement the logging policy via registry:

```
reg add "hklm\SOFTWARE\Policies\Microsoft\Windows\PowerShell\ScriptBlockLogging" /v EnableScriptBlockLogging /t REG_DWORD /d 1
```

Rule query

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event.category:process and
  powershell.file.script_block_text : (
    TVqQAAMAAAAEAAAA
  )

Framework: MITRE ATT&CK^TM

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/
Sub-technique:
- Name: PowerShell
- ID: T1059.001
- Reference URL: https://attack.mitre.org/techniques/T1059/001/

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