CVE-2013-0190 in Xen
Summary
by MITRE
The xen_failsafe_callback function in Xen for the Linux kernel 2.6.23 and other versions, when running a 32-bit PVOPS guest, allows local users to cause a denial of service (guest crash) by triggering an iret fault, leading to use of an incorrect stack pointer and stack corruption.
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Analysis
by VulDB Data Team • 04/22/2021
The vulnerability described in CVE-2013-0190 represents a critical flaw in the Xen hypervisor's handling of privilege level transitions within 32-bit paravirtualized guest operating systems. This issue specifically affects the xen_failsafe_callback function which serves as a critical component in the hypervisor's interrupt handling mechanism. The vulnerability arises from improper management of the stack pointer during interrupt return operations, creating a condition where local users within a guest operating system can manipulate the execution flow to trigger an iret fault. This fault condition causes the hypervisor to use an incorrect stack pointer, resulting in stack corruption that ultimately leads to guest system crashes and complete denial of service for the affected virtual machine. The flaw exists in the Linux kernel version 2.6.23 and subsequent releases, making it a long-standing issue that affects numerous virtualized environments. The vulnerability is particularly concerning because it operates at the hypervisor level, where local privilege escalation opportunities can be leveraged to compromise entire virtualized infrastructures.
The technical implementation of this vulnerability stems from a fundamental error in the xen_failsafe_callback function's handling of the interrupt return mechanism. When a 32-bit PVOPS (Paravirtualized Operating System) guest executes, the hypervisor must manage the transition between different privilege levels during interrupt processing. The flaw occurs when the iret instruction attempts to restore the processor state, including the stack pointer, but the hypervisor has corrupted or improperly calculated the stack pointer value. This mismanagement creates a scenario where the processor attempts to access memory locations that are either invalid or unauthorized, causing the guest operating system to crash. The vulnerability specifically affects systems where the guest operates in a 32-bit environment and utilizes paravirtualized drivers, making it particularly relevant to older virtualization deployments that have not been updated to newer versions of the Xen hypervisor. This issue is categorized under CWE-122, which deals with improper restriction of operations within a bounds, and falls under ATT&CK technique T1068, which involves exploit for privilege escalation.
The operational impact of CVE-2013-0190 extends beyond simple denial of service, as it represents a potential pathway for more sophisticated attacks within virtualized environments. When a guest system crashes due to this vulnerability, it can result in complete service interruption for applications running within that virtual machine, affecting availability of critical business services. In multi-tenant cloud environments, this vulnerability could allow malicious users to disrupt services for other tenants, potentially causing cascading failures across the virtualized infrastructure. The vulnerability is particularly dangerous in environments where guest operating systems are not regularly updated or patched, as it provides a consistent method for attackers to cause system instability. Organizations utilizing Xen hypervisors in production environments should consider this vulnerability as a potential attack vector for both disruption and information gathering activities, as system crashes can provide valuable information about the underlying virtualization infrastructure. The vulnerability's impact is amplified in containerized environments or those using shared virtual resources, where the stability of one guest system can affect the entire virtualized ecosystem.
Mitigation strategies for CVE-2013-0190 should focus on immediate patching of affected Xen hypervisor versions, as the vulnerability has been addressed through official security updates. Organizations should prioritize updating their hypervisor installations to versions that include fixes for this specific stack corruption issue, particularly those that address the improper handling of the iret instruction within the xen_failsafe_callback function. System administrators should implement monitoring solutions to detect potential exploitation attempts and establish automated alerting for guest system crashes that may indicate this vulnerability being targeted. Additional mitigations include implementing strict guest operating system updates and ensuring that virtualization environments are configured to use the latest available hypervisor patches. The vulnerability demonstrates the importance of maintaining up-to-date virtualization infrastructure and highlights the need for comprehensive security testing of hypervisor components, particularly those involved in privilege level transitions and interrupt handling mechanisms. Organizations should also consider implementing network segmentation and access controls to limit the potential impact of exploitation attempts, while maintaining detailed logging of hypervisor operations to facilitate forensic analysis in case of successful exploitation attempts.