arch/x86/ia32/ia32entry.S in the Linux kernel before 2.6.31.4 on the x86_64 platform does not clear certain kernel registers before a return to user mode, which allows local users to read register values from an earlier process by switching an ia32 process to 64-bit mode.
https://www.redhat.com/archives/fedora-package-announce/2009-October/msg00483.html
https://rhn.redhat.com/errata/RHSA-2010-0095.html
https://rhn.redhat.com/errata/RHSA-2010-0046.html
https://rhn.redhat.com/errata/RHSA-2009-1540.html
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A7359
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A10823
https://bugzilla.redhat.com/show_bug.cgi?id=526788
http://www.ubuntu.com/usn/usn-864-1
http://www.securityfocus.com/bid/36576
http://www.redhat.com/support/errata/RHSA-2009-1671.html
http://www.openwall.com/lists/oss-security/2009/10/02/1
http://support.avaya.com/css/P8/documents/100073666
http://secunia.com/advisories/37351
http://secunia.com/advisories/37075
http://secunia.com/advisories/36927
http://marc.info/?l=oss-security&m=125511635004768&w=2
http://marc.info/?l=oss-security&m=125444390112831&w=2
http://marc.info/?l=oss-security&m=125442304214452&w=2
http://lkml.org/lkml/2009/10/1/164
http://lists.opensuse.org/opensuse-security-announce/2010-02/msg00005.html
http://lists.opensuse.org/opensuse-security-announce/2009-11/msg00007.html
http://lists.opensuse.org/opensuse-security-announce/2009-11/msg00005.html