The kill_something_info function in kernel/signal.c in the Linux kernel before 2.6.28 does not consider PID namespaces when processing signals directed to PID -1, which allows local users to bypass the intended namespace isolation, and send arbitrary signals to all processes in all namespaces, via a kill command.
https://exchange.xforce.ibmcloud.com/vulnerabilities/50386
https://bugzilla.redhat.com/show_bug.cgi?id=496031
http://www.ubuntu.com/usn/usn-793-1
http://www.securityfocus.com/archive/1/503610/100/0/threaded
http://www.redhat.com/support/errata/RHSA-2009-1081.html
http://www.openwall.com/lists/oss-security/2009/04/21/1
http://www.openwall.com/lists/oss-security/2009/04/17/4
http://www.openwall.com/lists/oss-security/2009/04/16/2
http://www.kernel.org/pub/linux/kernel/v2.6/ChangeLog-2.6.28
http://www.debian.org/security/2009/dsa-1800
http://www.debian.org/security/2009/dsa-1787
http://wiki.rpath.com/Advisories:rPSA-2009-0084
http://secunia.com/advisories/35656
http://secunia.com/advisories/35343
http://secunia.com/advisories/35121
http://secunia.com/advisories/35120
http://secunia.com/advisories/34981