[Infowarrior] - DNS lords expose netizens to 'poisoning'

[Richard Forno]

DNS lords expose netizens to 'poisoning'
'A dumbfounding mystery'
By Dan Goodin in San Francisco → More by this author
Published Tuesday 15th April 2008 19:50 GMT

http://www.theregister.co.uk/2008/04/15/dns_cache_poisoning/

More than a decade after serious holes were discovered in the internet's
address lookup system, end users remain vulnerable to so-called domain name
system cache poisoning, a security researcher has warned.

Developers of the software that handles DNS lookups have scrambled to patch
buggy code that could allow the attacks, but not to the satisfaction of Amit
Klein, CTO of security firm Trusteer, who over the past year has uncovered
serious new vulnerabilities in multiple DNS products.

Last July, he exposed flaws in Berkeley Internet Name Domain (BIND), the
mostly widely used DNS server. The flaws allowed attackers to predict the
pseudo-random number transaction number that the software uses when
providing the numeric IP address of a requested web page. That, in turn,
could allow the attacker to supply a fraudulent address that leads to a
malicious destination.

"I'm not too comfortable with the quality of the solution from the security
and predictability standpoint," Klein said during a session at last week's
RSA security conference in San Francisco.

DNS lookups are one of the most basic and common tasks on the internet. They
translate human-friendly names such as theregister.co.uk with
machine-readable IP addresses like 212.100.234.54.

DNS cache poisoning first came to light in 1997, when researchers discovered
that an attacker could infect the DNS resolvers of internet service
providers and large organizations with spoofed IP addresses. The servers
store the incorrect information for hours or days at a time, so the attack
has the potential to send large numbers of end users to websites that
install malware or masquerade as a bank or other trusted destination and
steal sensitive account information.

In 1998, Eugene E. Kashpureff admitted to federal US authorities that on two
occasions the previous year he interrupted service for tens of thousands of
Internet users worldwide. By corrupting DNS caches, he was able to divert
traffic intended for InterNIC to AlterNIC, a competing domain name
registration site that he owned.

Makers of DNS products, which in addition to BIND's Internet System
Consortium, include Microsoft, PowerDNS and OpenBSD, responded to the
discovery by requiring look-up requests and responses to include
pseudo-random transaction ID numbers. Because attackers can't predict them,
DNS cache servers automatically ignore any attempts to send spoofed
responses. But over the past year, Klein has found defects in the
randomization processes of many of these products that allow him to
accurately predict the ID numbers.

That has prompted a new round of patches that include more robust
algorithms. Just last week, for instance, Microsoft pushed out a Windows
update that did just that. Klein hasn't had time to examine that patch, but
he's still not confident the transaction ID in others can't be predicted.

Asked how such a wide range of developers could deploy weak randomization
features into software so critical to the functioning of the net, Klein
said: "It's a mystery to me. None of them probably consulted a real
cryptography expert. There are DNS server implementations which use real
crypto, so it is not that they didn't have any counter examples. I'm as
dumbfounded by this as you are." ®