DHCP spoofing is a type of network attack where a malicious server attempts to provide false DHCP (Dynamic Host Configuration Protocol) information to clients on a network. This allows the attacker to intercept and potentially manipulate network traffic, often leading to a man-in-the-middle (MITM) attack.
How DHCP Spoofing Works:
The standard DHCP process involves a client broadcasting a request for network configuration (IP address, gateway, DNS server, etc.). A legitimate DHCP server then responds with an offer. A DHCP spoofing attack exploits this process:
- Rogue DHCP Server: The attacker sets up a rogue DHCP server on the network.
- DHCP Request Interception: When a client broadcasts a DHCP request, the rogue DHCP server quickly responds with an offer containing malicious configuration information.
- Malicious Configuration: This offer typically includes:
- Incorrect IP address: This can prevent the client from accessing the internet.
- Spoofed Default Gateway: The attacker sets themselves as the default gateway, allowing them to intercept all traffic from the client.
- Spoofed DNS Server: The attacker sets a malicious DNS server, allowing them to redirect users to phishing sites or other malicious websites.
- Man-in-the-Middle Attack: With the client now configured to use the attacker's system as the gateway or DNS server, the attacker can monitor, modify, or redirect network traffic.
Why is DHCP Spoofing Dangerous?
DHCP spoofing can have severe consequences:
- Data Theft: The attacker can capture sensitive information like usernames, passwords, and credit card details.
- Malware Infection: The attacker can redirect users to malicious websites that install malware on their systems.
- Denial of Service (DoS): The attacker can provide incorrect or conflicting IP addresses, preventing users from accessing the network.
- Phishing: The attacker can redirect users to fake login pages to steal their credentials.
Preventing DHCP Spoofing:
Several measures can be taken to prevent DHCP spoofing attacks:
- DHCP Snooping: This is a security feature on network switches that filters DHCP traffic, allowing only authorized DHCP servers to respond to requests. It maintains a trusted binding table and discards DHCP messages from untrusted sources.
- Port Security: Configuring port security on switches can prevent unauthorized devices from connecting to the network.
- Rogue DHCP Server Detection: Use network monitoring tools to identify unauthorized DHCP servers on the network. Regularly scan your network for unexpected DHCP servers.
- Physical Security: Restrict physical access to network infrastructure to prevent attackers from plugging in rogue DHCP servers.
- Static IP Addresses (Where Appropriate): For devices that don't frequently move, consider using static IP addresses to bypass the DHCP process altogether.
Example:
Imagine a coffee shop with free Wi-Fi. A hacker sets up a rogue DHCP server on the network. When a customer connects to the Wi-Fi, their device receives IP settings from the hacker's server, making the hacker's computer the "gateway" to the internet. The hacker can then see all of the customer's unencrypted web traffic, potentially stealing passwords or credit card information.
