The MITRE CVE dictionary describes this issue as:
The DNS stub resolver in the GNU C Library (aka glibc or libc6) before version 2.26, when EDNS support is enabled, will solicit large UDP responses from name servers, potentially simplifying off-path DNS spoofing attacks due to IP fragmentation.
Find out more about CVE-2017-12132 from the
MITRE CVE dictionary dictionary and
This issue only affects systems which use a remote recursive resolver and enable EDNS0, either with the “edns0” option in /etc/resolv.conf, or using the RES_USE_EDNS0 or RES_USE_DNSSEC resolver flags. The underlying issue affects recursive resolvers such as BIND and Unbound as well, and has to be fixed separately there.