CVE-2015-6927 in vzctl
Summary
by MITRE
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.
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Analysis
by VulDB Data Team • 06/19/2022
The vulnerability identified as CVE-2015-6927 resides within the vzctl utility version 4.9.4 and earlier, which is a critical component in OpenVZ container management systems. This flaw stems from an insecure method of determining virtual environment layout where the system relies on checking for the existence of root.hdd/DiskDescriptor.xml within the VE private directory. The vulnerability creates a path traversal and privilege escalation risk that allows local users within simfs containers to manipulate the root password of arbitrary ploop containers through a sophisticated symlink attack mechanism.
The technical implementation of this vulnerability involves a fundamental flaw in access control and file system validation. When vzctl processes virtual environments, it performs layout determination based on the presence of specific XML files within container directories. Attackers exploiting this vulnerability can create symbolic links pointing to the target ploop container's root.hdd file, effectively bypassing normal access controls and allowing them to modify critical system files. The attack vector specifically targets the root.hdd directory structure and leverages the trust model inherent in the container management system where local CT root users gain unauthorized access to ploop container resources.
This vulnerability has significant operational impact within virtualized environments, particularly in hosting and cloud infrastructure deployments where multiple tenants share the same physical hardware. The ability to change root passwords for arbitrary ploop containers represents a severe privilege escalation attack that can lead to complete system compromise. The attack demonstrates a clear path to unauthorized access of control panels and administrative interfaces, potentially enabling attackers to gain persistent access to critical infrastructure components. The vulnerability affects both security and operational integrity by allowing unauthorized users to manipulate container configurations and access sensitive data.
The attack methodology follows established patterns described in the attack technique framework where attackers leverage insufficient path validation to create malicious symbolic links. This approach aligns with common privilege escalation techniques documented in attack frameworks and represents a form of hard link or symbolic link manipulation. The vulnerability is classified under CWE-59 and CWE-22 in the Common Weakness Enumeration catalog, specifically addressing improper link resolution and path traversal issues. Organizations implementing OpenVZ containerization technologies must consider this vulnerability in their security posture assessments and risk management strategies. The recommended mitigation involves upgrading to vzctl version 4.9.4 or later, which implements proper file validation and access control mechanisms. Additionally, administrators should implement strict file system permissions and monitoring for suspicious symbolic link creation activities within container directories. Network segmentation and container isolation practices should be reinforced to limit the potential impact of such attacks, while regular security audits of container management systems can help identify and remediate similar vulnerabilities before exploitation occurs.