CVE-2016-4962 in Xen
Summary
by MITRE
The libxl device-handling in Xen 4.6.x and earlier allows local OS guest administrators to cause a denial of service (resource consumption or management facility confusion) or gain host OS privileges by manipulating information in guest controlled areas of xenstore.
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Analysis
by VulDB Data Team • 08/22/2022
The vulnerability identified as CVE-2016-4962 resides within the libxl device-handling functionality of the Xen hypervisor version 4.6.x and earlier releases. This flaw represents a critical security weakness that enables local administrators within guest operating systems to exploit the hypervisor's management interfaces. The vulnerability specifically targets xenstore, which serves as the central configuration database for hypervisor management operations and guest device information. When guest administrators manipulate device information stored within xenstore, they can trigger unpredictable behavior in the hypervisor's resource management systems.
The technical implementation of this vulnerability stems from insufficient validation and sanitization of device information provided by guest operating systems. The libxl library, responsible for device handling within Xen, fails to properly verify the integrity and legitimacy of data submitted through xenstore interfaces. This oversight creates opportunities for malicious actors to inject malformed or unexpected device parameters that can cause the hypervisor to consume excessive system resources or become confused about device management states. The vulnerability operates at the intersection of privilege escalation and resource exhaustion, allowing attackers to either overwhelm system resources or manipulate hypervisor behavior to gain unauthorized access to host privileges.
The operational impact of CVE-2016-4962 extends beyond simple denial of service scenarios, as it can potentially enable privilege escalation attacks against the underlying host operating system. Local guest administrators who possess administrative rights within their virtual machines can exploit this vulnerability to compromise the entire virtualization environment. The resource consumption aspect of the attack can lead to system instability, while the management facility confusion component can create opportunities for attackers to manipulate hypervisor state information and potentially execute arbitrary code with host privileges. This vulnerability directly relates to CWE-20, which addresses improper input validation, and demonstrates how inadequate sanitization of guest-controlled data can lead to severe security consequences.
From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1059, which involves executing malicious code through legitimate system interfaces, and T1068, which focuses on local privilege escalation. The attack vector leverages the trust relationship between hypervisor management interfaces and guest operating systems, exploiting the legitimate xenstore communication channels to perform unauthorized operations. Organizations utilizing affected Xen versions face significant risk of unauthorized access to host systems, potential data breaches, and complete compromise of virtualization infrastructure. The vulnerability's exploitation requires minimal privileges within guest environments, making it particularly dangerous as it can be leveraged by attackers who have already gained some level of access to virtual machines.
Mitigation strategies for CVE-2016-4962 involve immediate patching of Xen hypervisor installations to versions 4.7.0 and later, which contain the necessary fixes for the device-handling logic. System administrators should also implement strict xenstore access controls and monitor for unusual device configuration changes that might indicate exploitation attempts. Additional defensive measures include isolating guest operating systems through proper network segmentation and implementing hypervisor-level monitoring for resource consumption anomalies. The vulnerability highlights the importance of validating all guest-controlled data within hypervisor management interfaces and demonstrates the critical need for robust input sanitization in virtualization platforms. Organizations should also conduct comprehensive security assessments of their virtualization environments to identify potential exploitation vectors and ensure proper patch management procedures are in place to prevent similar vulnerabilities from being exploited in the future.