CVE-2016-1570 in Xen
Summary
by MITRE
The PV superpage functionality in arch/x86/mm.c in Xen 3.4.0, 3.4.1, and 4.1.x through 4.6.x allows local PV guests to obtain sensitive information, cause a denial of service, gain privileges, or have unspecified other impact via a crafted page identifier (MFN) to the (1) MMUEXT_MARK_SUPER or (2) MMUEXT_UNMARK_SUPER sub-op in the HYPERVISOR_mmuext_op hypercall or (3) unknown vectors related to page table updates.
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Analysis
by VulDB Data Team • 07/03/2022
The vulnerability identified as CVE-2016-1570 resides within the Xen hypervisor's implementation of privileged virtual machine (PV) superpage functionality in the file arch/x86/mm.c. This issue affects Xen versions 3.4.0, 3.4.1, and 4.1.x through 4.6.x, representing a significant security flaw that undermines the isolation properties of virtualized environments. The vulnerability stems from inadequate validation of page identifiers, specifically machine frame numbers (MFNs), when processing hypercall operations that manipulate memory management extensions.
The technical flaw manifests through three distinct attack vectors that exploit the MMUEXT_MARK_SUPER and MMUEXT_UNMARK_SUPER sub-operations within the HYPERVISOR_mmuext_op hypercall interface. These operations are designed to manage superpage mappings in the hypervisor's memory management system, but they fail to properly validate the machine frame numbers provided by local PV guests. This validation gap allows malicious guest operating systems to craft specially constructed page identifiers that can bypass normal memory access controls and potentially access memory regions they should not be able to reach.
The operational impact of this vulnerability is severe and multifaceted, encompassing information disclosure, denial of service, privilege escalation, and unspecified other consequences. Local PV guests can leverage this flaw to extract sensitive information from other virtual machines or the host system, effectively breaking the isolation guarantees that virtualization platforms are designed to maintain. The potential for privilege escalation means that attackers could gain elevated permissions within the virtualized environment, while the denial of service component can cause system instability or complete system crashes. This vulnerability directly violates the fundamental security principle of hypervisor isolation and represents a critical weakness in the memory management subsystem.
The vulnerability maps to CWE-125 in the Common Weakness Enumeration, which covers "Out-of-bounds Read," and CWE-20 in "Improper Input Validation," indicating that the root cause involves insufficient validation of input parameters. From an ATT&CK framework perspective, this vulnerability aligns with T1055.011 "Process Injection" and T1068 "Exploitation for Privilege Escalation" techniques, as attackers can exploit memory management flaws to gain elevated privileges within virtualized environments. The attack surface is particularly concerning because it affects local PV guests, meaning that even within a virtualized environment, a compromised guest can potentially attack other guests or the host system.
Mitigation strategies must address both immediate patching requirements and architectural improvements to prevent similar vulnerabilities. Organizations should immediately upgrade to patched versions of Xen hypervisor that resolve this vulnerability, as no effective workarounds exist for the core memory management flaw. System administrators should implement monitoring for unusual hypercall patterns and memory management operations that could indicate exploitation attempts. The vulnerability highlights the importance of rigorous input validation in hypervisor code and underscores the need for comprehensive security testing of memory management subsystems in virtualization platforms. Additionally, organizations should consider implementing hypervisor hardening measures and maintaining strict access controls to limit the potential impact of such vulnerabilities in their virtualized environments.