libzmq before 4.0.6 and 4.1.x before 4.1.1 allows remote attackers to conduct downgrade attacks and bypass ZMTP v3 protocol security mechanisms via a ZMTP v2 or earlier header.
https://github.com/zeromq/zeromq4-x/commit/b6e3e0f601e2c1ec1f3aac880ed6a3fe63043e51
https://github.com/zeromq/libzmq/issues/1273
http://www.debian.org/security/2015/dsa-3255
http://lists.opensuse.org/opensuse-updates/2015-06/msg00018.html
http://lists.fedoraproject.org/pipermail/package-announce/2015-May/159176.html