Updates released this week by the Internet Systems Consortium (ISC) for the DNS software BIND address two vulnerabilities, including a new high-severity issue that can be exploited remotely.
BIND 9.9.9-P3, 9.10.4-P3 and 9.11.0rc3 patch a previously undisclosed denial-of-service (DoS) flaw that can be exploited using specially crafted DNS request packets. The security hole, tracked as CVE-2016-2776, was uncovered by the ISC and affects all servers that can receive request packets from any source.
“Testing by ISC has uncovered a critical error condition which can occur when a nameserver is constructing a response. A defect in the rendering of messages into packets can cause named to exit with an assertion failure in buffer.c while constructing a response to a query that meets certain criteria,” ISC explained in its advisory. “This assertion can be triggered even if the apparent source address isn’t allowed to make queries (i.e. doesn’t match ‘allow-query’).”
Advance notifications about this vulnerability were sent out on September 14. There is no evidence that the weakness has been exploited in attacks, but users have been advised to update their BIND installations.
The latest BIND releases also patch a medium severity DoS issue (CVE-2016-2775) that was disclosed in mid-July.
“If the lightweight resolver is asked to resolve a query name which, when combined with a search list entry, exceeds the maximum allowable length, the server can terminate due to an error,” ISC described the flaw. “A server which is affected by this defect will terminate with a segmentation fault error, resulting in a denial of service to client programs attempting to resolve names.”
Users have been informed that the details of this vulnerability are publicly available in a bug repository operated by Red Hat.
Related: DoS Vulnerability Patched in BIND