GnuPG 1.4.x, 2.0.x, and 2.1.x treats a key flags subpacket with all bits cleared (no usage permitted) as if it has all bits set (all usage permitted), which might allow remote attackers to bypass intended cryptographic protection mechanisms by leveraging the subkey.
lists.opensuse.org/opensuse-updates/2013-10/msg00003.html
lists.opensuse.org/opensuse-updates/2013-10/msg00006.html
rhn.redhat.com/errata/RHSA-2013-1459.html
thread.gmane.org/gmane.comp.encryption.gpg.devel/17712/focus=18138
ubuntu.com/usn/usn-1987-1
www.debian.org/security/2013/dsa-2773
www.debian.org/security/2013/dsa-2774
www.openwall.com/lists/oss-security/2013/09/13/4
bugzilla.redhat.com/show_bug.cgi?id=1010137