What is Chargen Flood Attack?
A Chargen Flood attack is a form of Denial of Service (DoS) attack that leverages the Chargen service, which is part of a rarely used Character Generator Protocol (Chargen). The Chargen protocol, defined in RFC 864, was initially designed to assist in testing, debugging, and generating characters for network devices. The Chargen service typically listens on UDP port 19 and responds with a stream of data to any host that sends a request.
Detecting a Chargen Flood attack can be challenging as the traffic may seem normal, but indicators like sudden spikes in UDP traffic on port 19, unresponsive systems, and abnormal outbound traffic from devices running the Chargen service can signal malicious activity
How Does a Chargen Flood Attack Happen?
The attack takes advantage of the UDP protocol (User Datagram Protocol), which is connectionless and does not require a handshake like TCP Handshake.
Here is how the process unfolds:
Attack initiation: The attacker sends multiple small UDP packets to devices running the Chargen service, requesting character data.
Amplification: Each request is met with a large, random response, far exceeding the size of the initial request.
Reflection: Attackers often spoof the source IP address, making it appear that the request is coming from the target system. As a result, the Chargen service sends the response to the spoofed IP (the target), amplifying the traffic and overwhelming the network.
Flooding: The target system is bombarded with large volumes of random data, clogging its resources, and causing a Denial of Service (DoS) for legitimate users.
How to Prevent a Chargen Flood Attack?
While the Chargen service is outdated and should not be used in modern networks, some legacy systems may still have it enabled. There are several key steps to protect your network from a Chargen Flood attack:
Disable the Chargen Service: The most effective way to prevent this attack is to disable the Chargen protocol if it is not being used. Since it is rarely necessary in modern environments, shutting it down closes off the vulnerability.
- For Unix/Linux systems, this can be done by editing the /etc/inetd.conf file and commenting out the Chargen service.
- For Windows, check your firewall settings or use the command prompt to disable the service.
Implement Access Control Lists (ACLs): Restricting access to your network using firewalls and Access Control Lists can limit potential attack vectors. Block UDP traffic to and from port 19, the default port for the Chargen service, on your network perimeter.
Rate Limiting: Applying rate limiting to network devices helps prevent an overwhelming number of requests from being processed. By setting thresholds for incoming traffic, rate limiting restricts the volume of requests, thereby minimizing the potential for server overload during an attack. However, this technique alone may not fully prevent the attack and should be used in combination with other mitigation strategies, such as disabling the CHARGEN protocol or employing DDoS protection systems.
Monitor and Patch Legacy Systems: If you have legacy systems still using the Chargen service for any reason, ensure they are fully patched and up to date. Regularly review the need for such services and decommission them wherever possible.
