extracting-config-from-agent-tesla-rat

name	extracting-config-from-agent-tesla-rat
description	Extract embedded configuration from Agent Tesla RAT samples including SMTP/FTP/Telegram exfiltration credentials, keylogger settings, and C2 endpoints using .NET decompilation and memory analysis.
domain	cybersecurity
subdomain	malware-analysis
tags	["agent-tesla","rat","config-extraction","dotnet","malware-analysis","keylogger","credential-theft"]
version	1.0
author	mahipal
license	Apache-2.0

Extracting Config from Agent Tesla RAT

Overview

Agent Tesla is a .NET-based Remote Access Trojan (RAT) and keylogger that ranked among the top 10 malware variants in 2024, impacting 6.3% of corporate networks globally. It exfiltrates stolen credentials via SMTP email, FTP upload, Telegram bot API, or Discord webhooks. The malware configuration is embedded in the .NET assembly, typically obfuscated using string encryption, resource encryption, or custom loaders that decrypt and execute Agent Tesla in memory via .NET Reflection (fileless). Configuration extraction involves decompiling the .NET assembly with dnSpy or ILSpy, identifying the decryption routine for configuration strings, and extracting SMTP server addresses, credentials, FTP endpoints, Telegram bot tokens, and targeted applications.

Prerequisites

• dnSpy or ILSpy for .NET decompilation
• Python 3.9+ with dnlib or pythonnet for automated extraction
• de4dot for .NET deobfuscation
• Understanding of .NET IL code and Reflection
• Sandbox for dynamic analysis (ANY.RUN, CAPE)

Practical Steps

Step 1: Deobfuscate and Extract Configuration

#!/usr/bin/env python3
"""Extract Agent Tesla RAT configuration from .NET assemblies."""
import re
import sys
import json
import base64
import hashlib
from pathlib import Path


def extract_strings_from_dotnet(filepath):
    """Extract readable strings from .NET binary for config analysis."""
    with open(filepath, 'rb') as f:
        data = f.read()

    # Extract US (User Strings) heap from .NET metadata
    strings = []

    # Look for common Agent Tesla config patterns
    patterns = {
        "smtp_server": re.compile(rb'smtp[\.\-][\w\.\-]+\.\w{2,}', re.I),
        "email": re.compile(rb'[\w\.\-]+@[\w\.\-]+\.\w{2,}'),
        "ftp_url": re.compile(rb'ftp://[\w\.\-:/]+', re.I),
        "telegram_token": re.compile(rb'\d{8,10}:[A-Za-z0-9_-]{35}'),
        "telegram_chat": re.compile(rb'(?:chat_id=|chatid[=:])[\-]?\d{5,15}', re.I),
        "discord_webhook": re.compile(rb'https://discord\.com/api/webhooks/\d+/[\w-]+'),
        "password": re.compile(rb'(?:pass(?:word)?|pwd)[=:]\s*[\w!@#$%^&*]{4,}', re.I),
        "port": re.compile(rb'(?:port|smtp_port)[=:]\s*\d{2,5}', re.I),
    }

    results = {}
     name, pattern  patterns.items():
        matches = pattern.findall(data)
         matches:
            results[name] = [m.decode(, errors=)  m  matches]

    
    b64_pattern = re.()
    b64_decoded = []
       b64_pattern.finditer(data):
        :
            decoded = base64.b64decode(.group())
            text = decoded.decode(, errors=)
             text.isprintable()  (text) > :
                b64_decoded.append(text)
         Exception:
            

     b64_decoded:
        results[] = b64_decoded[:]

     results


 ():
    
    key = .fromhex(key_hex)
    
    decrypted_strings = []

    
    blob_pattern = re.()
       blob_pattern.finditer(data):
        blob = .group()
        
        decrypted = (b ^ key[i % (key)]  i, b  (blob))
        :
            text = decrypted.decode(, errors=)
             text.isprintable()  (text.strip()) > :
                decrypted_strings.append(text.strip())
         UnicodeDecodeError:
            

    
    sha256_key = hashlib.sha256(key).digest()

     decrypted_strings


 ():
    
    methods = []

     config.get():
        methods.append({
            : ,
            : config[],
            : config.get(, []),
        })

     config.get():
        methods.append({
            : ,
            : config[],
        })

     config.get():
        methods.append({
            : ,
            : config[],
            : config.get(, []),
        })

     config.get():
        methods.append({
            : ,
            : config[],
        })

     methods


 __name__ == :
     (sys.argv) < :
        ()
        sys.exit()

    config = extract_strings_from_dotnet(sys.argv[])
    methods = analyze_exfiltration_config(config)

    report = {: config, : methods}
    (json.dumps(report, indent=))

Validation Criteria

• Exfiltration method identified (SMTP/FTP/Telegram/Discord)
• Server addresses and credentials extracted from config
• Targeted applications list recovered
• Keylogger and screenshot capture settings documented
• Persistence mechanism identified
• IOCs suitable for network blocking extracted

References

• Splunk - Agent Tesla Detection and Analysis
• Qualys - Catching the RAT Agent Tesla
• ANY.RUN Agent Tesla Analysis
• Trustwave - Agent Tesla Novel Loader
• Malpedia - Agent Tesla