Suspicious Portable Executable Encoded in Powershell Scriptedit

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: 5 minutes

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

Maximum alerts per execution: 100

References:

Tags:

  • Elastic
  • Host
  • Windows
  • Threat Detection
  • Execution

Version: 4 (version history)

Added (Elastic Stack release): 7.16.0

Last modified (Elastic Stack release): 8.1.0

Rule authors: Elastic

Rule license: Elastic License v2

Investigation guideedit

## 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 queryedit

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

Threat mappingedit

Framework: MITRE ATT&CKTM

Rule version historyedit

Version 4 (8.1.0 release)
  • Formatting only
Version 3 (8.0.0 release)
  • Updated query, changed from:

    event.code:"4104" and powershell.file.script_block_text : (
    TVqQAAMAAAAEAAAA )