CVE-2012-4539 in Xen
Summary
by MITRE
Xen 4.0 through 4.2, when running 32-bit x86 PV guests on 64-bit hypervisors, allows local guest OS administrators to cause a denial of service (infinite loop and hang or crash) via invalid arguments to GNTTABOP_get_status_frames, aka "Grant table hypercall infinite loop DoS vulnerability."
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Analysis
by VulDB Data Team • 04/19/2021
The vulnerability identified as CVE-2012-4539 represents a critical denial of service weakness within the Xen hypervisor family affecting versions 4.0 through 4.2. This flaw specifically manifests when 32-bit paravirtualized guests operate on 64-bit hypervisor systems, creating a scenario where legitimate administrative actions within the guest operating system can trigger catastrophic system behavior. The vulnerability stems from improper validation of hypercall arguments within the grant table management subsystem, which serves as a fundamental component for memory sharing between hypervisor and guest operating systems.
The technical root cause of this vulnerability lies in the GNTTABOP_get_status_frames hypercall implementation within Xen's hypervisor layer. When malicious or malformed arguments are passed to this specific hypercall from a 32-bit guest operating system running on a 64-bit hypervisor, the system enters an infinite loop condition that consumes excessive CPU resources and ultimately leads to system hang or complete crash. This occurs because the hypervisor fails to properly validate the input parameters before processing them, allowing crafted invalid arguments to bypass normal execution flow and trigger the problematic code path. The vulnerability specifically affects the grant table management functionality that enables efficient memory sharing between domains, making it a core component of Xen's virtualization architecture.
From an operational perspective, this vulnerability presents significant risks to virtualized environments since it can be exploited by local administrators within guest operating systems who possess minimal privileges. The impact extends beyond simple service disruption to potentially compromising entire virtualized infrastructures, particularly in cloud computing and hosting environments where multiple tenants share the same physical hardware. The infinite loop condition can cause cascading failures across multiple virtual machines, leading to widespread service outages that are difficult to diagnose and recover from. Organizations running affected Xen versions face potential denial of service conditions that could be exploited by malicious actors to disrupt services or as part of broader attack campaigns targeting virtualized environments.
The vulnerability aligns with CWE-129, which addresses improper validation of input boundaries, and demonstrates characteristics consistent with ATT&CK technique T1499.004, which covers network denial of service attacks through hypervisor manipulation. Organizations should implement immediate mitigations including upgrading to Xen versions 4.3 or later where this vulnerability has been patched, implementing strict hypercall parameter validation at the hypervisor level, and monitoring for unusual CPU consumption patterns that might indicate exploitation attempts. Additionally, network segmentation and hypervisor access controls should be strengthened to limit potential attack vectors, while regular security assessments of virtualized environments should include specific checks for vulnerable Xen versions and proper implementation of hypervisor hardening measures.
This vulnerability serves as a critical reminder of the importance of proper input validation in hypervisor implementations and the potential for seemingly benign administrative functions to become attack vectors when not properly secured. The patch for this vulnerability required modifications to the hypercall argument validation logic within the grant table management code, ensuring that all input parameters are properly bounded and validated before processing. Organizations should prioritize upgrading their Xen installations and implementing comprehensive monitoring solutions that can detect anomalous behavior patterns consistent with this type of denial of service attack, as the vulnerability can be particularly challenging to detect and isolate due to its subtle nature and the fact that it requires legitimate administrative access within guest operating systems to exploit effectively.