Query: threat report mentioning Non-Application Layer Protocol
Matching passage: T1095 Non-Application Layer Protocol. Tactics: command and control. Description: Adversaries may use an OSI non-application layer protocol for communication between host and C2 server or among infected hosts within a network. The list of possible protocols is extensive.(Citation: Wikipedia OSI) Specific examples include use of network layer protocols, such as the Internet Control Message Protocol (ICMP), transport layer protocols, such as the User Datagram Protocol (UDP), session layer protocols, such as Socket Secure (SOCKS), as well as redirected/tunneled protocols, such as Serial over LAN (SOL). ICMP communication between hosts is one example.(Citation: Cisco Synful Knock Evolution) Because ICMP is part of the Internet Protocol Suite, it is required to be implemented by all IP-compatible hosts.(Citation: Microsoft ICMP) However, it is not as commonly monitored as other Internet Protocols such as TCP or UDP and may be used by adversaries to hide communications. In ESXi environments, adversaries may leverage the Virtual Machine Communication Interface (VMCI) for communication between guest virtual machines and the ESXi host. This traffic is similar to client-server communications on traditional network sockets but is localized to the physical machine running the ESXi host, meaning it does not traverse external networks (routers, switches). This results in communications that are invisible to external monitoring and standard networking tools like tcpdump, netstat, nmap, and Wireshark. By adding a VMCI backdoor to a compromised ESXi host, adversaries may persistently regain access from any guest VM to the compromised ESXi host’s backdoor, regardless of network segmentation or firewall rules in place.(Citation: Google Cloud Threat Intelligence VMWare ESXi Zero-Day 2023)
Near-miss passage: T1572 Protocol Tunneling. Tactics: command and control. Description: 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](https://attack.mitre.org/techniques/T1572) may also be abused by adversaries during [Dynamic Resolution](https://attack.mitre.org/techniques/T1568). 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](https://attack.mitre.org/techniques/T1572) in conjunction with [Proxy](https://attack.mitre.org/techniques/T1090) and/or [Protocol or Service Impersonation](https://attack.mitre.org/techniques/T1001/003) to further conceal C2 communications and infrastructure.