The flaw, rated as “high severity” (CVSS score of 7.5), is remotely exploitable in the case of servers uses certain configurations.

“Some configurations using both DNS64 and RPZ can lead to an INSIST assertion failure or a NULL pointer read; in either case named will terminate.” reads the advisory published by the ISC

“Under some conditions when using both DNS64 and RPZ [Response Policy Zones] to rewrite query responses, query processing can resume in an inconsistent state leading to either an INSIST assertion failure or an attempt to read through a NULL pointer,” 

Only servers utilizing both DNS64 and RPZ at the same time are potentially vulnerable.

“When this condition occurs, it will result in either an INSIST assertion failure (and subsequent abort) or an attempt to read through a NULL pointer. On most platforms a NULL pointer read leads to a segmentation fault (SEGFAULT), which causes the process to be terminated,” ISC added.

The advisory suggests to update each vulnerable installation, it also includes possible workarounds such as removing either DNS64 or RPZ from the configuration, or restricting the contents of the policy zone.

In January 2017, the Internet Systems Consortium (ISC) has issued updates to solve four high severity flaws in the DNS software BIND. The flaw could be exploited by a remote attacker to cause a DoS condition.

An attacker can exploit the vulnerabilities to cause the BIND name server process to encounter an assertion failure and stop executing.

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Pierluigi Paganini

(Security Affairs – BIND DNS software, security)