vzctl before 4.9.4 determines the virtual environment (VE) layout based on the presence of root.hdd/DiskDescriptor.xml in the VE private directory, which allows local simfs container (CT) root users to change the root password for arbitrary ploop containers, as demonstrated by a symlink attack on the ploop container root.hdd file and then access a control panel.

References

• https://nvd.nist.gov/vuln/detail/CVE-2015-6927
• https://openvz.org/Download/vzctl/4.9.4
• https://security.gentoo.org/glsa/201701-30
• https://src.openvz.org/projects/OVZL/repos/vzctl/commits/9e98ea630ac0e88b44e3e23c878a5166aeb74e1c
• http://www.debian.org/security/2015/dsa-3357