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Security researchers have discovered several serious new vulnerabilities in the BIND software that runs on the vast majority of the Internets DNS servers. The most serious flaw, a buffer overrun in both BIND 4 and BIND 8, enables an attacker to execute arbitrary code on a vulnerable server.
The Internet Software Consortium, which maintains the free BIND (Berkeley Internet Name Domain) software, has released patches for both affected versions.
An attacker who controls an authoritative DNS server can instruct BIND to cache DNS information in its internal database. In order for this to happen, the server must have recursion enabled, which is the default setting. There is a flaw in the formation of the responses that contain SIG resource records to requests for cached DNS information.
An attacker who exploited this flaw could execute any code of choice on the affected server, according to a bulletin published Tuesday by Internet Security Systems Inc.s X-Force research team.
BIND is by far the most popular software for running DNS servers, which serve as the Internets address book.
BIND 8 is also vulnerable to two separate denial-of-service attacks. The first vulnerability involves the way that BIND 8 servers handle some invalid DNS lookup requests. An attacker could attach an OPT resource record with a large UDP (user datagram packet) payload to a lookup request on a non-existent sub-domain of a valid domain. Such a request would cause a recursive server to fail.
The other DoS problem occurs when an attacker who controls a DNS server causes a vulnerable server running BIND 8 to cache SIG resource record elements with invalid expirations. The resource records are removed from the BIND internal database but then are later improperly referenced, which causes a denial of service.
ISC is in the process of building updated releases for both BIND 4 and 8. Versions 4.9.11 and 8.3.4 will be available soon. BIND 9 is not affected by any of these vulnerabilities, ISS said.