Zero-Day BIND Flaw Crashes DNS Servers

The Internet Systems Consortium (ISC) today issued a temporary patch for an as-yet unidentified flaw in the DNS BIND 9 platform that is causing servers around the Internet to crash.

Chaouki Bekrar, CEO and head of research at VUPEN, says the fixes don’t appear to repair the actual vulnerability, but rather prevent the DNS servers from crashing when handling the error generated by the bug.

ISC posted an advisory earlier today warning of a “serious” issue with BIND 9 name servers handling recursive queries. In what it characterized as an “as-yet unidentified network event,” servers were crashing after logging an error. “Organizations across the Internet reported crashes interrupting service on BIND 9 nameservers performing recursive queries. Affected servers crashed after logging an error in query.c with the following message: “INSIST(! dns_rdataset_isassociated(sigrdataset)),” ISC said in its advisory today.

The issue forces the servers to cache an invalid record and “subsequent queries [that] could crash the resolvers with an assertion failure,” the advisory says.

As of this posting, ISC had not revealed the underlying problem, but said the patches would prevent the servers from crashing. The flaw affects BIND 9.4-ESV, 9.6-ESV, 9.7.x, and 9.8.x.

The patch basically ensures that the cache doesn’t return the anomalous data and prevents the server from crashing.

VUPEN’s Bekrar says thus far, it’s unclear whether the servers were crashing due to exploitable code execution or a denial-of-service issue. In a tweet earlier today, VUPN said, “A serious vulnerability was found in the DNS software BIND. It is currently exploited in the wild to crash servers.”

But David Ulevitch, CEO of OpenDNS, says it’s likely a remote DoS flaw, but so far there’s not enough information to determine the fallout. “It’s not even clear if bad guys knew what was happening. It could just be a malformed DNS packet that crashes BIND,” Ulevitch says.

ISC in its advisory said active exploits are “under investigation,” but did not provide any further details aside from its advisory. The advisory and information on downloading the temporary patches are available here.

Srini Avirneni, vice president of customer advocacy and innovation at Nominum, says DNS is critical, so any time there’s a disruption, it’s a big deal. “Nominum tracks DNS events around the world and is aware there have been outages over the last 24 hours, although no Nominum customers experienced any outages. Because the DNS is so critical, these events always attract a lot of attention. Everyone depends on the Internet today, and when the DNS is down the Internet is effectively down,” Avirneni says.

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