The pit_ioport_read in i8254.c in the Linux kernel before 2.6.33 and QEMU before 2.3.1 does not distinguish between read lengths and write lengths, which might allow guest OS users to execute arbitrary code on the host OS by triggering use of an invalid index.
https://github.com/torvalds/linux/commit/ee73f656a604d5aa9df86a97102e4e462dd79924
https://bugzilla.redhat.com/show_bug.cgi?id=1229640
http://mirror.linux.org.au/linux/kernel/v2.6/ChangeLog-2.6.33
http://www.openwall.com/lists/oss-security/2015/06/25/7
https://security.gentoo.org/glsa/201510-02
http://www.securityfocus.com/bid/75273
https://www.mail-archive.com/[email protected]/msg304138.html
https://support.lenovo.com/product_security/qemu
http://www.securitytracker.com/id/1032598
https://support.lenovo.com/us/en/product_security/qemu
http://rhn.redhat.com/errata/RHSA-2015-1512.html
http://rhn.redhat.com/errata/RHSA-2015-1508.html
http://rhn.redhat.com/errata/RHSA-2015-1507.html
https://www.exploit-db.com/exploits/37990/
http://www.debian.org/security/2015/dsa-3348
https://www.arista.com/en/support/advisories-notices/security-advisories/1180-security-advisory-13