CVE-2014-5146 in Xen
Summary
by MITRE
Certain MMU virtualization operations in Xen 4.2.x through 4.4.x before the xsa97-hap patch, when using Hardware Assisted Paging (HAP), are not preemptible, which allows local HVM guest to cause a denial of service (vcpu consumption) by invoking these operations, which process every page assigned to a guest, a different vulnerability than CVE-2014-5149.
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Analysis
by VulDB Data Team • 02/10/2022
The vulnerability identified as CVE-2014-5146 represents a critical denial of service flaw within the Xen hypervisor's memory management unit virtualization subsystem. This weakness specifically affects Xen versions 4.2.x through 4.4.x prior to the implementation of the xsa97-hap patch, exposing systems to potential abuse by malicious local HVM (Hardware Virtual Machine) guests. The issue stems from the non-preemptible nature of certain Memory Management Unit operations when Hardware Assisted Paging is enabled, creating a scenario where guest operating systems can exploit this limitation to consume excessive virtual CPU resources.
The technical flaw manifests in the hypervisor's handling of MMU virtualization operations that utilize Hardware Assisted Paging functionality. When these operations are invoked, they process every page assigned to a guest virtual machine, creating a computationally intensive task that cannot be interrupted or preempted by the hypervisor's scheduling mechanisms. This design flaw allows a local HVM guest to trigger operations that iterate through all memory pages allocated to the guest, causing the virtual CPU to consume excessive processing time and system resources. The vulnerability specifically impacts the hypervisor's ability to maintain proper resource allocation and scheduling priorities, as these memory management operations lack the necessary preemption points required for responsive system operation.
From an operational perspective, this vulnerability enables local HVM guests to perform a denial of service attack against the host system by consuming excessive virtual CPU resources. The malicious guest can repeatedly invoke memory management operations that process every page in its assigned memory space, effectively starving other virtual machines and the hypervisor itself of processing power. This resource exhaustion can lead to system instability, reduced performance for other virtual guests, and potential complete system unresponsiveness. The impact extends beyond individual virtual machines to affect the entire hypervisor infrastructure, potentially compromising the availability of services running on the host system.
The vulnerability aligns with CWE-664, which addresses improper control of a resource through lifetime management, and relates to ATT&CK technique T1499.001 for resource exhaustion. The flaw demonstrates a classic example of insufficient preemption handling in virtualization environments, where the hypervisor fails to properly manage the execution of memory management operations that can monopolize CPU resources. Organizations running affected Xen versions should prioritize applying the xsa97-hap patch to address this vulnerability and restore proper resource management capabilities within the hypervisor's memory subsystem.
This vulnerability is distinct from CVE-2014-5149, which addresses different aspects of hypervisor memory management, but both issues highlight the complexity of virtualization security and the critical importance of proper resource management in hypervisor implementations. The combination of these vulnerabilities demonstrates the need for comprehensive security testing and patch management in virtualization environments to prevent local privilege escalation and denial of service attacks that can compromise entire infrastructure deployments.