DNS flaws put Net connected systems at risk

[InfoSec News <isn () c4i org>]

http://www.infoworld.com/articles/hn/xml/02/07/01/020701hndns.xml

By Joris Evers 
July 1, 2002 9:18 am PT

A FLAW IN software that supports the Internet's DNS (Domain Name
System) for translating text-based Web addresses to numeric IP
(Internet Protocol) addresses can put Internet-connected systems at
risk, experts warned.

The flaw lies in two versions of the DNS resolver library, which is
not only used in DNS servers, but also in network hardware such as
routers and switches, said Joost Pol, a security consultant at Pine
Internet in The Hague, Netherlands, on Monday.

"This code was written a long time ago and distributed for free, it is
widespread," said Pol, who wrote the first alert on the issue last
week. "This is essential software that runs on the client and on the
server."

Affected are the Berkeley Internet Name Domain (BIND) DNS resolver
library, developed by the Internet Software Consortium, and the
Berkeley Software Distribution (BSD) DNS resolver library, according
to an advisory released on Friday by the U.S.-based Computer Emergency
Response Team Coordination Center (CERT/CC).

A buffer overflow vulnerability in the libraries could allow a remote
attacker to take over systems using the affected software by sending a
malformed DNS response, according to CERT/CC. After a successful
attack on a router, for example, an attacker could tap or divert
traffic, said Pol.

Administrators should immediately check if their systems use any of
the vulnerable DNS resolver libraries and, if so, upgrade those, Pol
said, adding that this is not a simple job.

"This is living hell for an administrator," he said.

It is not just a question of checking which systems are vulnerable --
including server operating systems, DNS servers, e-mail servers,
switches and routers -- and then simply applying a patch. The
vulnerable library could be embedded in an application, which means an
administrator has to recompile the application, said Pol.

Only if applications dynamically link to the DNS resolver library can
the issue be solved by just updating the library, said Pol.

A solution suggested by CERT/CC is shielding vulnerable systems by
setting up an additional DNS server as a gatekeeper. This local
caching DNS server will prevent malicious DNS responses from reaching
systems using vulnerable DNS resolver libraries by reconstructing DNS
responses, CERT/CC said.

Pol however feels DNS caching can only be a temporary solution.

"There will always be a point that the additional DNS server is
switched off, for example when a new system administrator comes in,"  
he said.

Products that use the vulnerable DNS resolver libraries include the
various BSD operating systems and products from Cray., Network
Appliance and the Internet Software Consortium, according to a list
compiled by CERT/CC.

Microsoft says it does not use the affected libraries in its software,
according to the list, but Pol has his doubts.

"A lot of BSD code was used in Windows 2000, but if you believe
Microsoft, you have no problem," he said.

No exploit script to take advantage of the DNS resolver library flaws
is currently in public circulation, according to Pol and various
advisories addressing the issue. But it won't be long until computer
crackers come up with one, Pol warned. "I think work is being done on
exploits right now."



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