CVE 2009-1338
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.
See the 
CVE page on Mitre.org
for more details.
