CVE-2016-7466 in QEMU
Summary
by MITRE
Memory leak in the usb_xhci_exit function in hw/usb/hcd-xhci.c in QEMU (aka Quick Emulator), when the xhci uses msix, allows local guest OS administrators to cause a denial of service (memory consumption and possibly QEMU process crash) by repeatedly unplugging a USB device.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-7466 represents a critical memory management flaw within the QEMU virtualization platform, specifically affecting the usb_xhci_exit function in the hardware USB controller implementation. This issue manifests when the xhci (eXtensible Host Controller Interface) USB controller utilizes MSI-X (Message Signaled Interrupts) for interrupt handling, creating a persistent memory leak condition that can be exploited by malicious actors within the guest operating system. The vulnerability falls under the CWE-401 category of "Improper Release of Memory Before Removing Last Reference," indicating a fundamental flaw in resource management where allocated memory is not properly deallocated during the device removal process.
The technical implementation of this vulnerability occurs within the QEMU hypervisor's USB subsystem where the usb_xhci_exit function fails to correctly release memory resources associated with USB device contexts when devices are repeatedly unplugged from the xhci controller. This memory leak specifically affects the MSI-X interrupt handling mechanism, where each device removal operation should properly clean up allocated structures but instead retains references to memory blocks that accumulate over time. The flaw is particularly dangerous because it can be triggered through normal USB device operations, making it exploitable by any local administrator within the guest operating system without requiring special privileges or complex attack vectors.
The operational impact of this vulnerability extends beyond simple resource exhaustion, potentially leading to complete system instability and service disruption. When exploited repeatedly, the memory leak causes progressive memory consumption that can eventually exhaust available system resources, forcing the QEMU process to crash or become unresponsive. This creates a denial of service condition that affects not only the virtual machine hosting the compromised guest but also potentially impacts the host system's overall performance and stability. The vulnerability is particularly concerning in virtualized environments where multiple VMs may be running on the same host, as the cumulative effect of multiple memory leaks could lead to cascading failures and system-wide instability.
Mitigation strategies for this vulnerability require immediate implementation of QEMU updates and patches that address the specific memory management issue in the usb_xhci_exit function. System administrators should prioritize patching affected QEMU installations and consider implementing monitoring solutions to detect unusual memory consumption patterns that may indicate exploitation attempts. The vulnerability also highlights the importance of proper resource management in virtualization environments and the need for comprehensive testing of interrupt handling mechanisms in hypervisor components. Organizations should implement regular security assessments of their virtualization infrastructure and maintain up-to-date vulnerability management processes to prevent exploitation of similar memory-related flaws that could be leveraged for more sophisticated attacks. This vulnerability demonstrates the critical nature of proper memory management in hypervisor components and aligns with ATT&CK techniques focusing on resource exhaustion and denial of service attacks that can be executed through legitimate system operations.