CVE-2016-7422 in QEMU
Summary
by MITRE
The virtqueue_map_desc function in hw/virtio/virtio.c in QEMU (aka Quick Emulator) allows local guest OS administrators to cause a denial of service (NULL pointer dereference and QEMU process crash) via a large I/O descriptor buffer length value.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-7422 represents a critical denial of service flaw within the QEMU virtualization platform that affects the virtio subsystem's handling of I/O descriptor buffers. This issue resides in the virtqueue_map_desc function located in the hw/virtio/virtio.c source file, which is part of the QEMU hypervisor implementation that facilitates virtualized I/O operations between guest operating systems and host hardware. The vulnerability specifically manifests when a local guest OS administrator manipulates the I/O descriptor buffer length parameter to an excessively large value, creating a condition that leads to a NULL pointer dereference and subsequent crash of the QEMU process.
The technical exploitation of this vulnerability occurs through the improper validation of I/O descriptor buffer length parameters within the virtio driver implementation. When a guest operating system submits an I/O request with an abnormally large buffer length value, the virtqueue_map_desc function fails to adequately validate this input before attempting to process the descriptor. This lack of proper bounds checking creates a scenario where the function attempts to dereference a NULL pointer, resulting in an immediate process crash that terminates the QEMU instance hosting the affected virtual machine. The flaw stems from inadequate input sanitization and memory management practices within the virtualization layer, specifically in how the hypervisor handles guest-supplied I/O descriptor metadata.
From an operational perspective, this vulnerability poses significant risks to virtualized environments where guest operating systems may be compromised or where administrative privileges are available within the guest. The local nature of the attack means that an attacker with administrative access to a guest OS can exploit this flaw to crash the QEMU process, effectively causing a denial of service that impacts the entire virtual machine and potentially the host system. This vulnerability particularly affects cloud computing environments, virtual desktop infrastructures, and any deployment where multiple virtual machines share a single hypervisor instance, as a successful exploit could lead to service disruption across multiple tenants or virtual environments. The impact extends beyond simple service interruption, as such crashes can potentially lead to data loss or corruption if the QEMU process terminates during critical I/O operations.
The vulnerability maps to CWE-476 which describes NULL pointer dereference conditions, and aligns with ATT&CK technique T1499.004 for Network Denial of Service and T1059.001 for Command and Scripting Interpreter. Effective mitigation strategies include implementing proper input validation and bounds checking within the virtqueue_map_desc function to ensure that I/O descriptor buffer lengths remain within reasonable parameters. System administrators should also apply the latest QEMU security patches that address this specific vulnerability, as the maintainers have released fixes that properly validate descriptor buffer lengths and prevent the NULL pointer dereference condition. Additionally, deploying monitoring solutions that can detect anomalous I/O descriptor patterns and implementing virtual machine resource limits can help prevent exploitation of this vulnerability in production environments.
The broader implications of this vulnerability highlight the critical importance of input validation and memory safety in hypervisor implementations. Virtualization platforms must maintain rigorous security practices to prevent guest operating systems from compromising host stability, as these systems serve as the foundation for modern cloud computing and enterprise virtualization infrastructures. The vulnerability demonstrates that even seemingly benign I/O operations can become attack vectors when proper input validation is absent, emphasizing the need for comprehensive security testing and code review processes within virtualization software development. Organizations should also consider implementing additional security controls such as guest operating system hardening, privilege separation, and regular security audits to minimize the risk of similar vulnerabilities in their virtualized environments.