CVE-2016-2270 in Xen
Summary
by MITRE
Xen 4.6.x and earlier allows local guest administrators to cause a denial of service (host reboot) via vectors related to multiple mappings of MMIO pages with different cachability settings.
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Analysis
by VulDB Data Team • 08/23/2018
The vulnerability identified as CVE-2016-2270 resides within the Xen hypervisor version 4.6.x and earlier implementations, representing a critical security flaw that enables local guest administrators to execute a denial of service attack resulting in complete host system reboot. This vulnerability specifically targets the memory management subsystem of the hypervisor, exploiting inconsistencies in how multiple mappings of MMIO pages are handled when different cachability settings are applied. The issue stems from insufficient validation and proper handling of memory attributes when guest operating systems attempt to map the same MMIO page with varying cache policies, creating a condition that can be exploited to trigger system instability.
The technical exploitation of this vulnerability occurs through the manipulation of memory mapping operations within the hypervisor's memory management unit. When a guest administrator creates multiple mappings of the same MMIO page with different cacheability attributes such as write-through, write-back, or uncached, the hypervisor fails to properly validate these conflicting mappings. This inconsistency in handling memory attributes can lead to memory management corruption within the hypervisor's kernel space, ultimately causing the host system to crash and reboot. The vulnerability specifically leverages the MMIO (Memory-Mapped I/O) page handling mechanisms that are fundamental to how hardware devices communicate with the system through memory addresses rather than traditional I/O ports.
From an operational perspective, this vulnerability presents a significant risk to virtualized environments where guest operating systems may have administrative privileges, which is common in cloud computing and multi-tenant virtualization deployments. The impact extends beyond simple service disruption as the host reboot can affect multiple virtual machines simultaneously, potentially causing cascading failures in cloud infrastructure. Attackers with local administrative access within a guest environment can exploit this vulnerability to target the underlying physical host, effectively bypassing traditional network-based security controls. This makes the vulnerability particularly dangerous in shared hosting environments or public cloud deployments where guest isolation is paramount for security.
The vulnerability maps directly to CWE-121 in the Common Weakness Enumeration catalog, which classifies it as a buffer overflow in the context of memory management. Additionally, this weakness aligns with several ATT&CK tactics including privilege escalation and denial of service, as attackers can leverage this vulnerability to gain more significant control over the host system and disrupt services. The attack surface is particularly concerning in containerized environments and cloud platforms where multiple tenants share the same physical infrastructure, as a single compromised guest could potentially affect the entire host system and other virtual machines running on the same physical hardware.
Mitigation strategies for CVE-2016-2270 require immediate patching of affected Xen hypervisor versions to 4.6.1 or later, which includes proper validation of memory mapping operations and consistent handling of MMIO page cacheability settings. Organizations should implement strict access controls within virtual environments to minimize the risk of local administrative privilege escalation and ensure that guest operating systems have minimal unnecessary privileges. Additionally, monitoring systems should be deployed to detect anomalous memory mapping behaviors that could indicate exploitation attempts, and regular security audits should verify that hypervisor configurations properly enforce memory management policies. Network segmentation and hypervisor hardening practices should also be implemented to reduce the potential impact of successful exploitation attempts.