CVE-2011-1898 in Xen
Summary
by MITRE
Xen 4.1 before 4.1.1 and 4.0 before 4.0.2, when using PCI passthrough on Intel VT-d chipsets that do not have interrupt remapping, allows guest OS users to gain host OS privileges by "using DMA to generate MSI interrupts by writing to the interrupt injection registers."
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Analysis
by VulDB Data Team • 11/17/2021
This vulnerability exists in Xen hypervisor versions prior to 4.1.1 and 4.0.2, specifically affecting systems utilizing PCI passthrough with Intel VT-d chipsets lacking interrupt remapping capabilities. The flaw stems from insufficient isolation mechanisms between guest operating systems and the host system when handling DMA operations that generate MSI interrupts through direct writes to interrupt injection registers. The vulnerability is classified under CWE-264 as a privilege escalation issue and represents a critical security gap in virtualization environments where guest users can exploit hardware interaction mechanisms to compromise host system integrity.
The technical implementation of this vulnerability exploits the lack of proper interrupt remapping in VT-d chipsets, allowing malicious guest operating systems to manipulate DMA operations that would normally be restricted to host-level processes. When guest users write directly to interrupt injection registers, they can effectively bypass normal interrupt handling procedures and gain unauthorized access to host system resources. This occurs because the hypervisor fails to properly validate or restrict DMA write operations that could generate MSI interrupts, creating an attack vector where guest users can escalate privileges to host-level access. The vulnerability specifically targets the interaction between virtualization software and hardware interrupt handling mechanisms.
The operational impact of this vulnerability is severe as it enables complete compromise of the host system from within a guest environment. Attackers can leverage this privilege escalation to execute arbitrary code with host privileges, potentially leading to complete system takeover, data exfiltration, or further attacks on other virtual machines sharing the same physical host. The vulnerability affects organizations using Xen hypervisors in cloud computing environments, virtual desktop infrastructures, and any deployment where guest operating systems require direct hardware access through PCI passthrough. This represents a fundamental breakdown in hypervisor security boundaries, as documented in ATT&CK technique T1055 for privilege escalation through hypervisor attacks.
Mitigation strategies include upgrading to Xen versions 4.1.1 or 4.0.2 and later, which contain patches addressing the interrupt handling mechanisms. Organizations should also ensure that VT-d chipsets with interrupt remapping capabilities are deployed where possible, as this hardware feature provides essential protection against such attacks. Additionally, implementing strict access controls and monitoring for unusual DMA operations can help detect potential exploitation attempts. System administrators should disable PCI passthrough functionality when not required and maintain comprehensive logging of interrupt handling activities. The fix addresses the root cause by properly validating DMA write operations and ensuring that guest users cannot directly manipulate interrupt injection registers to gain unauthorized host privileges, aligning with security best practices for virtualization environments and compliance with industry standards for hypervisor security.