The ne2000_receive function in hw/net/ne2000.c in QEMU before 2.4.0.1 allows attackers to cause a denial of service (infinite loop and instance crash) or possibly execute arbitrary code via vectors related to receiving packets.
https://www.arista.com/en/support/advisories-notices/security-advisories/1188-security-advisory-14
https://lists.gnu.org/archive/html/qemu-devel/2015-09/msg05832.html
https://lists.gnu.org/archive/html/qemu-devel/2015-09/msg03985.html
http://www.ubuntu.com/usn/USN-2745-1
http://www.openwall.com/lists/oss-security/2015/09/15/2
http://lists.fedoraproject.org/pipermail/package-announce/2015-October/168671.html
http://lists.fedoraproject.org/pipermail/package-announce/2015-October/168646.html
http://lists.fedoraproject.org/pipermail/package-announce/2015-October/168077.html