CVE-2016-5008 in libvirt
Summary
by MITRE
libvirt before 2.0.0 improperly disables password checking when the password on a VNC server is set to an empty string, which allows remote attackers to bypass authentication and establish a VNC session by connecting to the server.
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Analysis
by VulDB Data Team • 09/02/2022
The vulnerability identified as CVE-2016-5008 affects libvirt versions prior to 2.0.0 and represents a critical authentication bypass flaw in virtual machine management systems. This issue specifically impacts the VNC server implementation within libvirt, where the software fails to properly validate password credentials when an empty string is provided as the password. The flaw stems from improper handling of authentication mechanisms, creating a security gap that allows unauthorized remote access to virtual machine consoles. This vulnerability is particularly concerning in virtualized environments where multiple tenants or administrators manage numerous virtual machines through libvirt's VNC interface.
The technical root cause of this vulnerability lies in the flawed implementation of password validation logic within libvirt's VNC server component. When a VNC password is explicitly set to an empty string, the system should enforce proper authentication checks or reject such insecure configurations. However, the vulnerable implementation allows connections to proceed without proper credential verification, effectively disabling authentication controls. This behavior aligns with CWE-312, which addresses the exposure of sensitive information through improper handling of credentials. The flaw demonstrates a classic case of insufficient input validation where the system fails to properly process edge cases in authentication parameters, leading to unintended access permissions.
The operational impact of CVE-2016-5008 extends beyond simple unauthorized access to virtual machine consoles. Attackers can leverage this vulnerability to establish full VNC sessions with administrative privileges, potentially leading to complete compromise of virtualized environments. This authentication bypass enables malicious actors to perform unauthorized actions such as accessing sensitive data within virtual machines, modifying configurations, executing arbitrary commands, or even escalating privileges within the virtualized infrastructure. The vulnerability affects organizations relying on libvirt for virtual machine management, particularly those using VNC interfaces for remote administration, creating significant risk exposure for cloud providers, data centers, and enterprise virtualization deployments.
Organizations should implement immediate mitigations including upgrading to libvirt version 2.0.0 or later, which contains the necessary patches to address the authentication bypass. System administrators should also review and enforce secure configuration practices for VNC servers, ensuring that empty passwords are not permitted and that strong authentication mechanisms are implemented. Network segmentation and firewall rules should be configured to limit access to VNC ports to trusted networks only, while additional monitoring should be implemented to detect unauthorized VNC connection attempts. The vulnerability demonstrates the importance of proper authentication implementation and highlights the need for comprehensive security testing of authentication mechanisms, particularly in systems handling sensitive virtualized environments. This issue also relates to ATT&CK technique T1078 which covers valid accounts and privilege escalation through unauthorized access to systems, making it a critical concern for organizations implementing virtualization security controls.