Adversaries may tunnel network communications to and from a victim system within a separate protocol to avoid detection/network filtering and/or enable access to otherwise unreachable systems. Tunneling involves explicitly encapsulating a protocol within another. This behavior may conceal malicious traffic by blending in with existing traffic and/or provide an outer layer of encryption (similar to a VPN). Tunneling could also enable routing of network packets that would otherwise not reach their intended destination, such as SMB, RDP, or other traffic that would be filtered by network appliances or not routed over the Internet. There are various means to encapsulate a protocol within another protocol. For example, adversaries may perform SSH tunneling (also known as SSH port forwarding), which involves forwarding arbitrary data over an encrypted SSH tunnel.(Citation: SSH Tunneling)(Citation: Sygnia Abyss Locker 2025) Protocol Tunneling may also be abused by adversaries during Dynamic Resolution. Known as DNS over HTTPS (DoH), queries to resolve C2 infrastructure may be encapsulated within encrypted HTTPS packets.(Citation: BleepingComp Godlua JUL19) Adversaries may also leverage Protocol Tunneling in conjunction with Proxy and/or Protocol or Service Impersonation to further conceal C2 communications and infrastructure.
launchd or user-invoked processes (ssh, socat) encapsulating traffic via SSH tunnels, VPN-style tooling, or DNS-over-HTTPS clients. Defender sees outbound TLS traffic with embedded DNS or RDP payloads.
sshd, socat, or custom binaries initiating port forwarding or encapsulating traffic (e.g., RDP, SMB) through SSH or HTTP. Defender sees abnormal connect/bind syscalls, encrypted traffic on ports typically used for non-encrypted services, and outlier traffic volume patterns.
Processes such as plink.exe, ssh.exe, or netsh.exe establishing outbound network connections where traffic patterns show encapsulated protocols (e.g., RDP over SSH). Defender observations include anomalous process-to-network relationships, large asymmetric data flows, and port usage mismatches.
Network Intrusion Prevention
Use intrusion detection signatures to block traffic at network boundaries.
Filter Network Traffic
Employ network appliances and endpoint software to filter ingress, egress, and lateral network traffic. This includes protocol-based filtering, enforcing firewall rules, and blocking or restricting traffic based on predefined conditions to limit adversary movement and data exfiltration. This mitigation can be implemented through the following measures: Ingress Traffic Filtering: - Use Case: Configure network firewalls to allow traffic only from authorized IP addresses to public-facing servers. - Implementation: Limit SSH (port 22) and RDP (port 3389) traffic to specific IP ranges. Egress Traffic Filtering: - Use Case: Use firewalls or endpoint security software to block unauthorized outbound traffic to prevent data exfiltration and command-and-control (C2) communications. - Implementation: Block outbound traffic to known malicious IPs or regions where communication is unexpected. Protocol-Based Filtering: - Use Case: Restrict the use of specific protocols that are commonly abused by adversaries, such as SMB, RPC, or Telnet, based on business needs. - Implementation: Disable SMBv1 on endpoints to prevent exploits like EternalBlue. Network Segmentation: - Use Case: Create network segments for critical systems and restrict communication between segments unless explicitly authorized. - Implementation: Implement VLANs to isolate IoT devices or guest networks from core business systems. Application Layer Filtering: - Use Case: Use proxy servers or Web Application Firewalls (WAFs) to inspect and block malicious HTTP/S traffic. - Implementation: Configure a WAF to block SQL injection attempts or other web application exploitation techniques.