The Internet Systems Consortium has issued a warning that certain
versions of BIND are vulnerable to a denial of service attack. BIND
is the most widely used domain name system protocol
implementation.
The latest version of BIND, 9.7.3, is not affected, but versions
9.7.1 through 9.7.2-P3 are vulnerable. Attackers could exploit the
vulnerability to create a denial of service attack because of the
way that BIND handles incremental zone transfers (IXFR), which is a
technique for transferring data on top of the transmission control
protocol (TCP).
"When an authoritative server processes a successful IXFR transfer
or a dynamic update, there is a small window of time during which
the IXFR/update -- coupled with a query -- may cause a deadlock to
occur," according to the ISC's security advisory issued on Tuesday.
"This deadlock will cause the server to stop processing all
requests. A high query rate and/or a high update rate will increase
the probability of this condition."
According to the ISC, this severe vulnerability can be remotely
exploited, although no related attacks have been seen in the
wild.
DNS is the technique used to resolve domain names into IP
addresses. Accordingly, security experts are urging any
organizations running a vulnerable version of BIND to upgrade
immediately. "IXFRs between authoritative name servers are a vital
part of keeping DNS both alive and correct," said Paul Ducklin head
of technology for antivirus firm Sophos in the Asia-Pacific region,
in a blog post.
With 300,000 new computers being connected to the Internet every
day, as well as the role of DNS in supporting cloud computing, its
importance continues to increase. "DNS servers are at the heart of
many cloud-style security services, providing the mechanism by
which up-to-date blocklist data is published," said Ducklin.
He also noted that Apple OS X includes a copy of BIND, though most
people don't run it. Even if they do, however, the latest Mac
operating system, OS X 10.6.6, includes the older BIND 9.6, which
is not vulnerable to the above exploit. "Sometimes, being behind
the curve is a good thing," he said.