Adversaries may redirect network traffic to adversary-owned systems by spoofing Dynamic Host Configuration Protocol (DHCP) traffic and acting as a malicious DHCP server on the victim network. By achieving the adversary-in-the-middle (AiTM) position, adversaries may collect network communications, including passed credentials, especially those sent over insecure, unencrypted protocols. This may also enable follow-on behaviors such as Network Sniffing or Transmitted Data Manipulation.
DHCP is based on a client-server model and has two functionalities: a protocol for providing network configuration settings from a DHCP server to a client and a mechanism for allocating network addresses to clients.(Citation: rfc2131) The typical server-client interaction is as follows:
The client broadcasts a DISCOVER message.
The server responds with an OFFER message, which includes an available network address.
The client broadcasts a REQUEST message, which includes the network address offered.
The server acknowledges with an ACK message and the client receives the network configuration parameters.
Adversaries may spoof as a rogue DHCP server on the victim network, from which legitimate hosts may receive malicious network configurations. For example, malware can act as a DHCP server and provide adversary-owned DNS servers to the victimized computers.(Citation: new_rogue_DHCP_serv_malware)(Citation: w32.tidserv.g) Through the malicious network configurations, an adversary may achieve the AiTM position, route client traffic through adversary-controlled systems, and collect information from the client network.
DHCPv6 clients can receive network configuration information without being assigned an IP address by sending a <code>INFORMATION-REQUEST (code 11)</code> message to the <code>All_DHCP_Relay_Agents_and_Servers</code> multicast address.(Citation: rfc3315) Adversaries may use their rogue DHCP server to respond to this request message with malicious network configurations.
Rather than establishing an AiTM position, adversaries may also abuse DHCP spoofing to perform a DHCP exhaustion attack (i.e, Service Exhaustion Flood) by generating many broadcast DISCOVER messages to exhaust a network’s DHCP allocation pool.
Detect DHCP Spoofing Across Linux, Windows, and macOS
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:
Egress Traffic Filtering:
Protocol-Based Filtering:
Network Segmentation:
Application Layer Filtering:
Network Intrusion Prevention: Use intrusion detection signatures to block traffic at network boundaries.