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.
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.
dnlib or pythonnet for automated extraction#!/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 = {}
for name, pattern in patterns.items():
matches = pattern.findall(data)
if matches:
results[name] = [m.decode('utf-8', errors='replace') for m in matches]
# Extract Base64-encoded strings (common obfuscation)
b64_pattern = re.compile(rb'[A-Za-z0-9+/]{20,}={0,2}')
b64_decoded = []
for match in b64_pattern.finditer(data):
try:
decoded = base64.b64decode(match.group())
text = decoded.decode('utf-8', errors='strict')
if text.isprintable() and len(text) > 5:
b64_decoded.append(text)
except Exception:
pass
if b64_decoded:
results["base64_decoded_strings"] = b64_decoded[:30]
return results
def decrypt_agenttesla_strings(data, key_hex):
"""Decrypt Agent Tesla encrypted configuration strings."""
key = bytes.fromhex(key_hex)
# Agent Tesla V1: Simple XOR with key
decrypted_strings = []
# Find encrypted blobs (high-entropy byte sequences)
blob_pattern = re.compile(rb'[\x80-\xff]{16,256}')
for match in blob_pattern.finditer(data):
blob = match.group()
# Try XOR decryption
decrypted = bytes(b ^ key[i % len(key)] for i, b in enumerate(blob))
try:
text = decrypted.decode('utf-8', errors='strict')
if text.isprintable() and len(text.strip()) > 3:
decrypted_strings.append(text.strip())
except UnicodeDecodeError:
pass
# V2: SHA256-based key derivation then AES
sha256_key = hashlib.sha256(key).digest()
return decrypted_strings
def analyze_exfiltration_config(config):
"""Analyze extracted configuration for exfiltration methods."""
methods = []
if config.get("smtp_server"):
methods.append({
"type": "SMTP",
"servers": config["smtp_server"],
"emails": config.get("email", []),
})
if config.get("ftp_url"):
methods.append({
"type": "FTP",
"urls": config["ftp_url"],
})
if config.get("telegram_token"):
methods.append({
"type": "Telegram",
"tokens": config["telegram_token"],
"chat_ids": config.get("telegram_chat", []),
})
if config.get("discord_webhook"):
methods.append({
"type": "Discord",
"webhooks": config["discord_webhook"],
})
return methods
if __name__ == "__main__":
if len(sys.argv) < 2:
print(f"Usage: {sys.argv[0]} <agent_tesla_sample>")
sys.exit(1)
config = extract_strings_from_dotnet(sys.argv[1])
methods = analyze_exfiltration_config(config)
report = {"raw_config": config, "exfiltration_methods": methods}
print(json.dumps(report, indent=2))