Character Generator Protocol: Difference between revisions

Revision as of 13:31, 28 October 2013

Revision as of 18:11, 14 November 2013

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The service was used maliciously to crash MS DNS servers running Microsoft Windows NT 4.0 by piping the arbitrary characters straight into the DNS server listening port (telnet ntbox 19 | telnet ntbox 53).<ref>{{cite web|url=http://support.microsoft.com/kb/169461 |title=Access Violation in Dns.exe Caused by Malicious Telnet Attack |publisher=Support.microsoft.com |date=2006-11-01 |accessdate=2009-05-31}}</ref> However, the attack was presumably a symptom of improper buffer management on the part of Microsoft's DNS service and not directly related to the CHARGEN service.{{Citation needed|date=August 2010}}

UDP CHARGEN is commonly used in denial of service attacks. By using a fake source address the attacker can send bounce traffic off a UDP CHARGEN application to the victim. UDP CHARGEN sends 200 to 1,000 times times more data than it receives, depending upon the implementation. This "traffic multiplication" is attractive to an attacker. Also attractive is the obscuring of the attacker's IP address from the victim.

CHARGEN was widely implemented on network-connected printers, and as printer firmware is rarely updated there are still many network-connected printers which implement the protocol. Where these are visible to the Internet they are invariably misused as denial of service vectors, as potential attackers often scan networks looking for UDP port 19 CHARGEN sources.