Re: weaknesses in dns label decoding,

From: bobk (bobkat_private)
Date: Mon May 31 1999 - 14:49:53 PDT


On Sun, 30 May 1999, Sebastian wrote:

>
> keywords: some dns packet decoders (sniffers, ids systems (?), dns
>           servers) may be vulnerable to malformed compressed domain names
>           inside dns packets.
>
> sorry aleph1, if this has already been known or posted =)
>
>
> hi,
>
> as I played with the DNS RFC (1035 especially) i came up with the idea to
> create malformed compressed dns domains inside the DNS packet to make it
> impossible for the DNS packet decoder to decompress it, which might lead
> to a denial of service attack.

Another thing to remember is that it is possible to put ABSOLUTELY
ANYTHING inside a DNS domain name. This includes whitespace, control
characters, and even NULL.

Imagine what could happen if some program did a strcmp() on the following
name:

rs.internic.net\0.xa.net

where, of course, \0 is a null

Interested readers may ponder what type of programs may be exploited with
this type of attack.



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