[Snort-sigs] Issue with rule sid 255

Brian bmc at ...95...
Fri Apr 25 06:31:09 EDT 2003


On Tue, Apr 22, 2003 at 10:50:08AM -0500, Geoff Craig wrote:
> I am having an issue with the TCP DNS Zone transfer rule included in the
> 2.0 distribution.  Unless I remove both the offset and the flow
> keywords, the rule never fires.  The environment I am in has all Windows
> 2000/2003 DNS servers.  The rule used to look like this;  (apologizes
> for the wrap)

Can you send pcap for that?

IFAIK, the zone transfer query type should actually be at least 16 bytes 
from the beginning of the packet.

  2 bytes (length)
+ 2 bytes (transaction id)
+ 2 bytes (flags)
+ 2 bytes (questions)
+ 2 bytes (answer RRs)
+ 2 bytes (authority RRs)
+ 2 bytes (additional RRs)
+ 1 byte  (count for the first label) [0]

We look for the label terminating byte (0x00) followed by the AXFR request 
(0x00fc). Simple math tells us our offset needs to be 15.  

Can you send me pcap for what this does?

[0] since this is a zone transfer, they have to ask for the zone, so
    we know there is going to be at least one label.

-brian




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