[NEWS] Multiple DNS Implementation DoS

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  Multiple DNS Implementation DoS
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SUMMARY

The Domain Name System (DNS) protocol "is an Internet service that 
translates domain names into Internet Protocol (IP) addresses. Because 
domain names are alphabetic, they're easier to remember, however the 
Internet is really based on IP addresses; hence every time a domain name 
is requested, a DNS service must translate the name into the corresponding 
IP address".

A vulnerability was found with the recursion process used by some DNS 
implementations to decompress compressed DNS messages. Under certain 
circumstances, it is possible to cause the DNS server to terminate 
abnormally.

DETAILS

The text portions of DNS messages are specified by first giving the 
character count, followed by the characters themselves. For example to 
specify 'test.test.com', the message would look like 
'0x04test0x04test0x03com0x00' using 16-bit numbers. From RFC1035, Section 
4.1.4 "Message Compression" specifies a way to create smaller messages so 
that they can easily fit into a DNS UDP packet. Hence if the top two bits 
of the label length byte are 1, the remaining 14 bits specify an offset 
from the beginning of the text on where the remaining characters can be 
found. This way, redundant information can be removed and hence create a 
smaller message.

Given this type of DNS message, the most obvious method to decode it is by 
using recursion. However consider a message that contains a code that 
instructs the DNS process to go to an illegal address once the end of the 
string is reached; if recursion is used to decode such a message, some DNS 
implementation may enter into a loop and eventually exhaust the stack. If 
this happens, then it would be possible for the DNS service to terminate 
and hence cause a denial-of-service condition.

CVE Information:
 <http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-0036> 
CAN-2005-0036
 <http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-0037> 
CAN-2005-0037
 <http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-0038> 
CAN-2005-0038


ADDITIONAL INFORMATION

The information has been provided by  <mailto:[email protected]> 
g0tcha.
The original article can be found at:  
<http://www.niscc.gov.uk/niscc/docs/al-20050524-00433.html> 
http://www.niscc.gov.uk/niscc/docs/al-20050524-00433.html



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