Anthropic-Cybersecurity-Skills/skills/detecting-suspicious-powershell-execution/scripts/agent.py

#!/usr/bin/env python3
"""Agent for detecting suspicious PowerShell execution patterns."""

import argparse
import json
import os
import re
import subprocess
import sys
from datetime import datetime, timezone


SUSPICIOUS_CMDLETS = [
    "Invoke-Expression", "IEX", "Invoke-WebRequest", "Invoke-RestMethod",
    "Start-Process", "New-Object Net.WebClient", "DownloadString",
    "DownloadFile", "System.Reflection.Assembly", "FromBase64String",
    "Invoke-Mimikatz", "Invoke-Shellcode", "Invoke-DllInjection",
    "Invoke-ReflectivePEInjection", "Get-Keystrokes", "Get-GPPPassword",
    "Invoke-CredentialInjection", "Invoke-TokenManipulation",
    "Add-Exfiltration", "Get-TimedScreenshot",
]

OBFUSCATION_PATTERNS = [
    (r'\-[eE][nN][cC]\s', "Encoded command (-enc)"),
    (r'[Ff][Rr][Oo][Mm][Bb][Aa][Ss][Ee]64', "Base64 decoding"),
    (r'\$\{[^}]+\}', "Variable obfuscation ${...}"),
    (r"'[^']*'\s*\+\s*'[^']*'", "String concatenation obfuscation"),
    (r'\-[Ww]indow[Ss]tyle\s+[Hh]idden', "Hidden window execution"),
    (r'\-[Nn]o[Pp]rofile', "NoProfile flag"),
    (r'\-[Ee]xecution[Pp]olicy\s+[Bb]ypass', "Execution policy bypass"),
    (r'[Ss]et-[Mm]pPreference.*-[Dd]isable', "Defender bypass attempt"),
    (r'[Aa][Mm][Ss][Ii]', "AMSI reference"),
]


def parse_script_block_logs():
    """Parse PowerShell script block logging events (Event ID 4104)."""
    events = []
    if sys.platform != "win32":
        return events
    ps_cmd = (
        "Get-WinEvent -FilterHashtable @{LogName='Microsoft-Windows-PowerShell/Operational';"
        "Id=4104} -MaxEvents 200 | Select-Object TimeCreated,"
        "@{N='ScriptBlock';E={$_.Properties[2].Value}},"
        "@{N='Path';E={$_.Properties[4].Value}} | ConvertTo-Json -Depth 3"
    )
    try:
        result = subprocess.check_output(
            ["powershell", "-NoProfile", "-Command", ps_cmd],
            text=True, errors="replace", timeout=30
        )
        data = json.loads(result) if result.strip() else []
        return data if isinstance(data, list) else [data]
    except (subprocess.SubprocessError, json.JSONDecodeError):
        return []


def analyze_script_content(script_text):
    """Analyze a PowerShell script for suspicious patterns."""
    findings = []
    if not script_text:
        return findings

    for cmdlet in SUSPICIOUS_CMDLETS:
        if cmdlet.lower() in script_text.lower():
            findings.append({"type": "suspicious_cmdlet", "cmdlet": cmdlet})

    for pattern, desc in OBFUSCATION_PATTERNS:
        if re.search(pattern, script_text):
            findings.append({"type": "obfuscation", "pattern": desc})

    b64_match = re.findall(r'[A-Za-z0-9+/]{40,}={0,2}', script_text)
    for b64 in b64_match[:3]:
        try:
            import base64
            decoded = base64.b64decode(b64).decode("utf-8", errors="replace")
            if any(c.lower() in decoded.lower() for c in SUSPICIOUS_CMDLETS[:10]):
                findings.append({"type": "encoded_payload", "preview": decoded[:100]})
        except Exception:
            pass

    return findings


def analyze_log_file(log_path):
    """Analyze a text file containing PowerShell commands."""
    findings = []
    try:
        with open(log_path, "r", errors="replace") as f:
            content = f.read()
        results = analyze_script_content(content)
        if results:
            findings.append({
                "file": log_path,
                "indicators": results,
                "indicator_count": len(results),
            })
    except FileNotFoundError:
        print(f"[!] File not found: {log_path}")
    return findings


def main():
    parser = argparse.ArgumentParser(
        description="Detect suspicious PowerShell execution patterns"
    )
    parser.add_argument("--event-logs", action="store_true",
                        help="Parse Windows PowerShell event logs")
    parser.add_argument("--script", help="Analyze a PowerShell script file")
    parser.add_argument("--log-dir", help="Directory of PS log files to scan")
    parser.add_argument("--output", "-o", help="Output JSON report")
    parser.add_argument("--verbose", "-v", action="store_true")
    args = parser.parse_args()

    print("[*] Suspicious PowerShell Execution Detection Agent")
    report = {"timestamp": datetime.now(timezone.utc).isoformat(), "findings": []}

    if args.event_logs:
        events = parse_script_block_logs()
        for evt in events:
            script = evt.get("ScriptBlock", "")
            indicators = analyze_script_content(script)
            if indicators:
                report["findings"].append({
                    "source": "event_log",
                    "time": evt.get("TimeCreated", ""),
                    "path": evt.get("Path", ""),
                    "indicators": indicators,
                    "preview": script[:200] if args.verbose else "",
                })
        print(f"[*] Analyzed {len(events)} script block events")

    if args.script:
        findings = analyze_log_file(args.script)
        report["findings"].extend(findings)

    if args.log_dir and os.path.isdir(args.log_dir):
        for root, _, files in os.walk(args.log_dir):
            for f in files:
                if f.lower().endswith((".ps1", ".psm1", ".psd1", ".log", ".txt")):
                    findings = analyze_log_file(os.path.join(root, f))
                    report["findings"].extend(findings)

    report["total_suspicious"] = len(report["findings"])
    report["risk_level"] = (
        "CRITICAL" if len(report["findings"]) >= 10
        else "HIGH" if len(report["findings"]) >= 5
        else "MEDIUM" if report["findings"]
        else "LOW"
    )
    print(f"[*] Suspicious findings: {len(report['findings'])}")

    if args.output:
        with open(args.output, "w") as f:
            json.dump(report, f, indent=2)
        print(f"[*] Report saved to {args.output}")
    else:
        print(json.dumps(report, indent=2))


if __name__ == "__main__":
    main()