CVE-2011-0011 in qemu
Summary
by MITRE
qemu-kvm before 0.11.0 disables VNC authentication when the password is cleared, which allows remote attackers to bypass authentication and establish VNC sessions.
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Analysis
by VulDB Data Team • 01/20/2025
The vulnerability identified as CVE-2011-0011 affects qemu-kvm versions prior to 0.11.0 and represents a critical authentication bypass flaw in the Virtual Network Computing implementation. This issue arises from a design flaw in how the virtualization platform handles VNC authentication when passwords are removed or cleared from the configuration. The vulnerability specifically manifests when the VNC password is unset or cleared, causing the system to disable authentication mechanisms entirely, thereby allowing unauthorized remote access to virtual machine console sessions.
The technical implementation of this flaw stems from improper state management within the qemu-kvm VNC subsystem. When administrators clear or remove VNC passwords from their virtual machine configurations, the underlying code fails to properly validate that authentication should remain enabled. This creates a scenario where the system transitions from a secured state to an unsecured state without proper authentication enforcement, effectively opening the virtual machine console to any remote attacker who can establish a VNC connection. The flaw operates at the protocol level where VNC authentication is disabled when password fields are empty or null, creating a dangerous default behavior that undermines the security model of virtual machine isolation.
From an operational impact perspective, this vulnerability represents a severe risk to virtualized environments as it allows remote attackers to gain direct console access to virtual machines without authentication. Attackers can exploit this by simply connecting to the VNC port of affected virtual machines, potentially gaining access to sensitive data, executing arbitrary code, or performing malicious activities within the virtual environment. The vulnerability is particularly concerning in cloud computing and data center environments where multiple virtual machines may be running with weak or no VNC authentication, creating a potential attack surface that could lead to widespread compromise of virtualized infrastructure.
The flaw aligns with CWE-305 authentication bypass weakness and can be mapped to several ATT&CK techniques including T1071.001 for application layer protocol usage and T1046 for network service scanning. Organizations utilizing affected qemu-kvm versions face significant risk of unauthorized access to virtual machine console sessions, potentially leading to data breaches, system compromise, and violation of compliance requirements. The vulnerability demonstrates poor input validation and state management practices, where the system fails to properly validate that authentication should remain active even when password fields are cleared or empty.
Mitigation strategies for this vulnerability include immediate upgrade to qemu-kvm version 0.11.0 or later, where the authentication bypass has been resolved. Administrators should also implement network-level controls such as firewall rules to restrict access to VNC ports, ensuring that only authorized networks can connect to virtual machine console services. Additional measures include implementing strong VNC password policies, enabling TLS encryption for VNC connections, and regularly auditing virtual machine configurations to ensure authentication mechanisms remain properly enforced. Organizations should also consider implementing network segmentation and monitoring solutions to detect unauthorized VNC connection attempts and establish proper incident response procedures for potential exploitation of this vulnerability.