chargen is the new DDoS tool?

Bernhard Schmidt berni at birkenwald.de
Tue Jun 11 15:39:32 UTC 2013


Heya everyone,

we have been getting reports lately about unsecured UDP chargen servers
in our network being abused for reflection attacks with spoofed sources

http://en.wikipedia.org/wiki/Character_Generator_Protocol

| In the UDP implementation of the protocol, the server sends a UDP
| datagram containing a random number (between 0 and 512) of characters
| every time it receives a datagram from the connecting host. Any data
| received by the server is discarded.

We are seeing up to 1500 bytes of response though.

This seems to be something new. There aren't a lot of systems in our
network responding to chargen, but those that do have a 15x
amplification factor and generate more traffic than we have seen with
abused open resolvers.

Anyone else seeing that? Anyone who can think of a legitimate use of
chargen/udp these days? Fortunately I can't, so we're going to drop
19/udp at the border within the next hours.

Regards,
Bernhard




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