Detect Encrypted Channel in Google Chronicle
This detection identifies adversaries using custom or non-standard encryption to conceal command and control (C2) traffic. Unlike legitimate TLS/HTTPS, malware implementing encrypted channels often exhibits behavioral anomalies: unusual processes making encrypted connections, connections to raw IP addresses without SNI, self-signed or short-lived certificates, high-frequency beaconing intervals, non-browser processes using port 443/8443 with atypical TLS fingerprints (JA3), and data volumes inconsistent with the application type. This detection correlates process lineage, network destinations, certificate characteristics, and traffic timing to surface encrypted C2 channels used by threat actors such as Tropic Trooper, Lazarus Group, and malware families including RCSession, Cryptoistic, Gomir, and Chaes.
MITRE ATT&CK
- Tactic
- Command and Control
- Technique
- T1573 Encrypted Channel
- Canonical reference
- https://attack.mitre.org/techniques/T1573/
YARA-L Detection Query
rule T1573_encrypted_channel {
meta:
author = "Detection Engineering"
description = "Detects potential encrypted C2 channels from non-browser processes"
severity = "high"
confidence = "medium"
mitre_attack = "T1573"
reference = "https://attack.mitre.org/techniques/T1573/"
events:
$e.metadata.event_type = "NETWORK_CONNECTION"
$e.network.direction = "OUTBOUND"
$e.target.port in (443, 8443, 4443, 8080, 9443)
not $e.principal.process.file.full_path = /chrome|firefox|msedge|outlook|teams|onedrive|slack|zoom/i
not re.regex($e.target.ip, `^(10\.|172\.(1[6-9]|2[0-9]|3[01])\.|192\.168\.|127\.)`)
condition:
$e
}Google Chronicle YARA-L 2.0 detection for Encrypted Channel. Detects encrypted C2 channels by identifying non-browser processes making encrypted connections (ports 443, 8443, etc.) to external IPs, particularly connections to raw IP addresses without hostname r
Data Sources
Required Tables
False Positives & Tuning
- Custom internal monitoring agents making encrypted connections to authorized services
- IT management tools with scheduled encrypted check-ins to management infrastructure
- Security products (EDR, DLP) with regular beaconing over encrypted channels
- Cloud sync and backup applications connecting to storage endpoints at intervals
- VPN clients maintaining persistent encrypted tunnel connections
Other platforms for T1573
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Simulate Custom Encrypted C2 Beacon Using PowerShell SSL
Expected signal: Sysmon Event ID 3 (NetworkConnect) with Image=powershell.exe, DestinationPort=443, DestinationHostname=ifconfig.me; Sysmon Event ID 1 showing PowerShell execution with -ExecutionPolicy Bypass flag; DeviceNetworkEvents showing 5 connections at ~30 second intervals (low jitter beaconing pattern)
- Test 2Simulate C2 Connection to Raw IP Address Over HTTPS
Expected signal: Sysmon Event ID 3 with Image=powershell.exe, DestinationIp=1.1.1.1, DestinationPort=443, DestinationHostname empty or equal to the IP address; DeviceNetworkEvents showing IsIPOnlyConnection=true with RemoteUrl matching RemoteIP
- Test 3Simulate Encrypted C2 Beacon from LOLBin (mshta.exe)
Expected signal: Sysmon Event ID 1 showing mshta.exe execution with HTA file path argument; Sysmon Event ID 3 with Image=mshta.exe, DestinationPort=443, DestinationHostname=httpbin.org; DeviceProcessEvents and DeviceNetworkEvents correlation showing mshta.exe as initiating process
- Test 4Linux Custom Encrypted Beacon Simulation Using OpenSSL
Expected signal: Auditd SYSCALL records for connect() calls from openssl process; syslog entries showing openssl process network activity; on hosts with Sysmon for Linux, Event ID 3 showing openssl making TLS connections to external IP on port 443 at ~30 second intervals
References (9)
- https://attack.mitre.org/techniques/T1573/
- https://www.secureworks.com/research/bronze-president-targets-southeast-asia
- https://www.sentinelone.com/labs/lazarus-on-the-hunt-for-big-game/
- https://symantec-enterprise-blogs.security.com/threat-intelligence/troll-stealer-golang
- https://www.cybereason.com/blog/chaes-malware-targets-brazils-banking-customers
- https://www.trendmicro.com/en_us/research/20/e/tropic-trooper-s-back-usbferry-attack-targets-air-gapped-environments.html
- https://engineering.salesforce.com/tls-fingerprinting-with-ja3-and-ja3s-247362855967/
- https://www.sans.org/white-papers/36277/
- https://github.com/salesforce/ja3
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