The following flaw was found in the nginx resolver: CNAME resolution was insufficiently limited, allowing an attacker who is able to trigger arbitrary name resolution to cause excessive resource consumption in worker processes. This issue affects nginx only if the "resolver" directive is used in a configuration file. The problems are fixed in nginx upstream versions 1.9.10 and 1.8.1. External References: http://mailman.nginx.org/pipermail/nginx-announce/2016/000169.html
Created nginx tracking bugs for this issue: Affects: fedora-all [bug 1302592]
Upstream commit: https://trac.nginx.org/nginx/changeset/93d70d87914c350948ab701cc99569680320e198/nginx
The nginx' DNS resolver is not enabled by default. It can be used to dynamically resolve names of backend servers. Therefore, in many configurations, attacker would not be able to make nginx resolve names in attacker controlled domain (backend servers and their name are usually considered trusted) without being able to MITM DNS traffic between nginx and configured DNS server (or the configured DNS server/resolver and authoritative DNS servers for the zone with names being resolved). If resolver is not used, backend server names specified in configuration are resolved to IP addresses at start.
This issue has been addressed in the following products: Red Hat Software Collections for Red Hat Enterprise Linux 7.2 EUS Red Hat Software Collections for Red Hat Enterprise Linux 7.1 EUS Red Hat Software Collections for Red Hat Enterprise Linux 7 Red Hat Software Collections for Red Hat Enterprise Linux 6 Red Hat Software Collections for Red Hat Enterprise Linux 6.6 EUS Red Hat Software Collections for Red Hat Enterprise Linux 6.7 EUS Via RHSA-2016:1425 https://access.redhat.com/errata/RHSA-2016:1425