VServer versions 1.27 and below (Linux 2.4 stable branch), 1.3.9 and below (Linux 2.4 devel branch), and 1.9.1 and below (Linux 2.6 devel branch) all allow for modifications to the proc filesystem that inadvertently propagate to the real underlying OS.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/33715/vserverProcFS.txt
Source: https://packetstormsecurity.com/files/33715/vserverProcFS.txt.html