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: 1. The client broadcasts a `DISCOVER` message. 2. The server responds with an `OFFER` message, which includes an available network address. 3. The client broadcasts a `REQUEST` message, which includes the network address offered. 4. 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.
Detects rogue DHCP activity by monitoring syslog for dhclient messages assigning unauthorized DNS/gateway values. Packet capture or IDS can detect multiple competing DHCP OFFERs from non-authorized servers.
Detects DHCP spoofing by monitoring unified logs for unexpected DHCP ACK/OFFER parameters and correlating with packet captures for multiple DHCP servers. Behavioral emphasis is on inconsistent DNS and gateway assignments that redirect traffic.
Detects rogue DHCP server activity and anomalous DHCP OFFER/ACK messages assigning unexpected DNS or gateway values. Detection correlates DHCP server role changes, DHCP exhaustion warnings, and sudden network configuration changes across endpoints.
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.