Qemu before 1.6.2 block diver for the various disk image formats used by Bochs and for the QCOW version 2 format, are vulnerable to a possible crash caused by signed data types or a logic error while creating QCOW2 snapshots, which leads to incorrectly calling update_refcount() routine.
git.qemu.org/?p=qemu.git%3Ba=commitdiff%3Bh=246f65838d19db6db55bfb41117c35645a2c4789
rhn.redhat.com/errata/RHSA-2014-0420.html
rhn.redhat.com/errata/RHSA-2014-0421.html
www.openwall.com/lists/oss-security/2014/03/26/8
bugzilla.redhat.com/show_bug.cgi?id=1078848
bugzilla.redhat.com/show_bug.cgi?id=1086717