CVE-2016-5403 in Xen
Summary
by MITRE
The virtqueue_pop function in hw/virtio/virtio.c in QEMU allows local guest OS administrators to cause a denial of service (memory consumption and QEMU process crash) by submitting requests without waiting for completion.
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Analysis
by VulDB Data Team • 03/14/2019
The vulnerability identified as CVE-2016-5403 resides within the QEMU virtualization platform's virtio subsystem, specifically in the virtqueue_pop function located in hw/virtio/virtio.c. This flaw represents a critical security issue that affects virtualized environments where guest operating systems maintain administrative privileges. The vulnerability stems from insufficient validation of request processing within the virtual I/O queue mechanism that QEMU employs to facilitate communication between guest and host systems. When a guest OS administrator submits requests to the virtio queue without properly awaiting their completion, the function fails to adequately handle such scenarios, leading to unpredictable behavior within the virtualization layer.
The technical exploitation of this vulnerability occurs through a specific pattern of queue management that bypasses normal completion handling procedures. In virtio implementations, guest operating systems submit I/O requests to virtual queues that are processed by the hypervisor. The virtqueue_pop function is responsible for retrieving and processing these requests from the queue. When requests are submitted without proper waiting for completion, the function enters an inconsistent state where it may consume excessive memory resources or trigger a segmentation fault leading to a complete QEMU process crash. This behavior fundamentally undermines the stability of the virtualization environment and can be leveraged by malicious actors with administrative access within the guest OS to disrupt service availability.
From an operational perspective, this vulnerability presents a significant threat to virtualized infrastructure security and reliability. Local guest OS administrators who possess administrative privileges can exploit this flaw to cause denial of service conditions that affect the entire virtualization platform. The memory consumption aspect of the vulnerability can lead to gradual resource exhaustion, while the process crash component can result in immediate service interruption. This type of vulnerability directly impacts the availability and integrity of virtualized environments, potentially affecting multiple virtual machines running on the same hypervisor host. The impact extends beyond individual VMs to encompass the broader virtualization infrastructure, as QEMU process crashes can affect all VMs hosted on that particular hypervisor instance.
The vulnerability aligns with CWE-400, which addresses "Uncontrolled Resource Consumption" and CWE-119, which covers "Improper Access to Resources via Virtual Resources." From an ATT&CK framework perspective, this vulnerability maps to T1499.004, "Evasion: Virtualization/Sandbox Evasion" and T1059.001, "Command and Scripting Interpreter: PowerShell." The flaw represents a classic example of how insufficient input validation and resource management can create exploitable conditions within virtualization environments. Security practitioners should note that this vulnerability is particularly concerning because it requires only local administrative access within the guest OS to exploit, making it accessible to attackers who have already gained some level of system control. The remediation approach involves implementing proper queue management protocols that ensure requests are handled appropriately regardless of their completion timing, including proper memory deallocation and state management within the virtqueue_pop function.
Mitigation strategies for CVE-2016-5403 should focus on both immediate patching and architectural improvements. Organizations must ensure that all QEMU installations are updated to versions containing the appropriate fixes for this vulnerability. The patch typically involves strengthening the validation logic within the virtqueue_pop function to properly handle cases where requests are submitted without waiting for completion. Additionally, system administrators should implement monitoring solutions that can detect unusual memory consumption patterns or process crashes that may indicate exploitation attempts. Network segmentation and access control measures should be reinforced to limit guest OS administrative privileges where possible, reducing the attack surface for this type of vulnerability. Regular security assessments of virtualization environments should include specific checks for similar queue management flaws that could present analogous security risks to the overall infrastructure.