The search_make_new function in evdns.c in libevent before 2.1.6-beta allows attackers to cause a denial of service (out-of-bounds read) via an empty hostname.
https://access.redhat.com/errata/RHSA-2017:1104
https://access.redhat.com/errata/RHSA-2017:1106
https://access.redhat.com/errata/RHSA-2017:1201
https://github.com/libevent/libevent/blob/release-2.1.6-beta/ChangeLog
https://github.com/libevent/libevent/commit/ec65c42052d95d2c23d1d837136d1cf1d9ecef9e
https://github.com/libevent/libevent/issues/332
https://security.gentoo.org/glsa/201705-01
http://www.debian.org/security/2017/dsa-3789
http://www.openwall.com/lists/oss-security/2017/01/31/17