The (1) fw_cfg_write and (2) fw_cfg_read functions in hw/nvram/fw_cfg.c in QEMU before 2.4, when built with the Firmware Configuration device emulation support, allow guest OS users with the CAP_SYS_RAWIO privilege to cause a denial of service (out-of-bounds read or write access and process crash) or possibly execute arbitrary code via an invalid current entry value in a firmware configuration.
https://security.gentoo.org/glsa/201604-01
https://lists.gnu.org/archive/html/qemu-devel/2016-01/msg00428.html
http://www.securitytracker.com/id/1034858
http://www.securityfocus.com/bid/80250
http://www.oracle.com/technetwork/topics/security/linuxbulletinjan2016-2867209.html
http://www.openwall.com/lists/oss-security/2016/01/12/11
http://www.openwall.com/lists/oss-security/2016/01/12/10
http://www.openwall.com/lists/oss-security/2016/01/11/7
http://www.debian.org/security/2016/dsa-3471
http://www.debian.org/security/2016/dsa-3470
http://www.debian.org/security/2016/dsa-3469
http://rhn.redhat.com/errata/RHSA-2016-0088.html
http://rhn.redhat.com/errata/RHSA-2016-0087.html
http://rhn.redhat.com/errata/RHSA-2016-0086.html
http://rhn.redhat.com/errata/RHSA-2016-0085.html
http://rhn.redhat.com/errata/RHSA-2016-0084.html
http://rhn.redhat.com/errata/RHSA-2016-0083.html