Updates released on Monday by the Internet Systems Consortium (ISC) for BIND, the most widely used DNS software, address a medium severity vulnerability.
The flaw, tracked as CVE-2016-2775, is related to the use of the lightweight resolver protocol (lwresd) to resolve names. Lwresd, which is similar but different from the normal DNS protocols, can be used via the lwresd utility in BIND or by configuring named with the lwres statement in named.conf.
Systems that use this method for name resolutions can be caused the enter a denial-of-service (DoS) condition due to an error in the way the protocol has been implemented in BIND.
“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 said in its advisory.
The remotely exploitable vulnerability affects BIND versions 9.0.x through 9.9.9-P1, 9.10.0 through 9.10.4-P1, and 9.11.0a3 through 9.11.0b1. ISC addressed the issue with the release of BIND 9.9.9-P2 and 9.10.4-P2.
ISC says there is no evidence that the vulnerability has been exploited in the wild, but noted that the flaw has been publicly disclosed in a Red Hat bug repository.
ISC security officer Michael McNally explained that the organization could not provide much advance notice to packagers as it was forced to accelerate its disclosure due to the availability of proof-of-concept (PoC) code in a public bug repository.
The new BIND releases include some regression fixes, but users who only want the fix for CVE-2016-2775 can request a standalone patch.