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A common way for malware to disguise its C2 communication and stay under the radar is by mimicking widely accepted protocols such as TLS, blending into existing traffic. The deep dive into PebbleDash’s FakeTLS C2 protocol reveals how North Korean APTs fake TLS handshakes and use hardcoded RC4 encryption to evade detection.
Read the full analysis here:
https://malwareandstuff.com/reversing-pebbledash-faketls-protocol/
You Should Know:
1. Detecting FakeTLS Traffic with Wireshark
FakeTLS often mimics legitimate TLS handshakes but lacks proper certificate validation. Use Wireshark to inspect traffic:
tshark -r suspicious_traffic.pcap -Y "tls.handshake.type == 1" -T fields -e ip.src -e ip.dst
Look for:
- Unusual Client Hello patterns
- Hardcoded RC4 cipher suites
- Repeated handshake failures
2. Extracting RC4 Keys from Memory (Volatility)
If you suspect FakeTLS malware, dump process memory and search for hardcoded keys:
volatility -f memory.dump --profile=Win10x64_19041 malfind --output=json
Search for RC4 key patterns (e.g., `\x01\x23\x45\x67\x89\xAB\xCD\xEF`).
3. Decrypting FakeTLS Traffic with Python
If you capture encrypted C2 traffic, use this Python snippet to decrypt RC4:
from Crypto.Cipher import ARC4
key = b"HardcodedKeyFromMemory"
cipher = ARC4.new(key)
decrypted = cipher.decrypt(encrypted_data)
print(decrypted.decode('utf-8', errors='ignore'))
4. Hunting FakeTLS in Windows Logs
Check for suspicious Schannel events (Event ID 36870-36888):
Get-WinEvent -FilterHashtable @{LogName='System'; ID=36870,36888} | Where-Object {$_.Message -match "RC4"}
5. YARA Rule for PebbleDash Detection
rule PebbleDash_FakeTLS {
meta:
description = "Detects PebbleDash FakeTLS implants"
strings:
$client_hello = "16 03 01 00 {5-10} 01 00" // Fake TLS Client Hello
$rc4_key = "01 23 45 67 89 AB CD EF"
condition:
any of them
}
What Undercode Say:
FakeTLS is a growing evasion technique used by APTs like PebbleDash. To defend:
– Monitor TLS anomalies (e.g., unexpected RC4 usage).
– Inspect memory for hardcoded keys.
– Use network segmentation to limit lateral movement.
– Update YARA/Sigma rules regularly.
Expected Output:
[+] Detected FakeTLS handshake from 192.168.1.100 [+] RC4 key found in process memory: \x01\x23\x45\x67... [+] Decrypted C2 payload: "cmd /c whoami"
For further reading:
References:
Reported By: Andreasklopsch Reversing – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
