CVE-2016-9911 in QEMU
Summary
by MITRE
Quick Emulator (Qemu) built with the USB EHCI Emulation support is vulnerable to a memory leakage issue. It could occur while processing packet data in 'ehci_init_transfer'. A guest user/process could use this issue to leak host memory, resulting in DoS for a host.
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Analysis
by VulDB Data Team • 10/12/2022
The vulnerability identified as CVE-2016-9911 affects Quick Emulator QEMU when configured with USB EHCI (Enhanced Host Controller Interface) emulation support. This represents a critical memory management flaw that exists within the virtualization layer of the emulator, specifically in how it handles USB packet data processing during the ehci_init_transfer function. The issue stems from inadequate memory boundary checks and improper handling of guest-controlled data inputs that flow through the USB emulation subsystem. When a malicious guest user or process exploits this vulnerability, it can trigger unintended memory access patterns that allow the guest environment to read portions of the host system's memory space. This memory leakage occurs because the emulator fails to properly validate or sanitize USB packet data before processing it within the EHCI transfer initialization routine. The flaw manifests as a potential information disclosure vulnerability where sensitive host memory contents could be exposed to the guest environment, though the primary impact observed is denial of service rather than direct privilege escalation.
The technical execution of this vulnerability requires a guest user to manipulate USB packet data in a specific manner that triggers the memory leakage condition within the ehci_init_transfer function. This type of vulnerability falls under the CWE-125 weakness category, which describes out-of-bounds read conditions where software reads data past the boundaries of allocated memory buffers. The attack vector operates through the USB EHCI controller emulation, where guest operating systems can send malformed or specially crafted USB packets that cause the emulator to access memory locations beyond the intended buffer boundaries. From an operational perspective, this vulnerability represents a significant concern for virtualization environments where multiple guest operating systems share the same host system resources. The potential for a guest to cause a host system crash or resource exhaustion through memory leakage creates a serious reliability risk that could affect other virtual machines running on the same physical host.
The impact of this vulnerability extends beyond simple denial of service conditions as it represents a fundamental flaw in the memory management practices within the QEMU USB emulation subsystem. Attackers could potentially leverage this weakness to gather sensitive information from the host system's memory, though the documented behavior primarily results in system instability and resource exhaustion. The vulnerability affects systems where QEMU is configured with EHCI USB controller emulation enabled, making it particularly relevant for desktop virtualization environments, cloud computing platforms, and development environments that rely on USB device passthrough functionality. From a threat modeling perspective, this vulnerability aligns with ATT&CK technique T1059.001 for command and script interpreter usage, as attackers could potentially use memory leakage to identify system configurations or sensitive data patterns. The flaw demonstrates poor input validation practices and inadequate bounds checking within the USB packet processing pipeline, creating a pathway for guest users to manipulate host memory access patterns through legitimate USB device interactions.
Mitigation strategies for CVE-2016-9911 should focus on immediate patch application from QEMU maintainers, as well as architectural modifications to reduce the attack surface. Organizations should disable USB EHCI emulation in QEMU configurations when not required for specific use cases, and implement proper memory access controls within virtualized environments. The fix typically involves adding proper bounds checking and input validation to the ehci_init_transfer function to prevent out-of-bounds memory access patterns. System administrators should also consider implementing monitoring solutions to detect unusual memory access patterns or excessive resource consumption that could indicate exploitation attempts. Additionally, network segmentation and virtual machine isolation practices can help limit the potential impact of successful exploitation attempts, while regular security audits of virtualization configurations can help identify similar memory management vulnerabilities in other subsystems. The vulnerability underscores the importance of proper memory safety practices in virtualization software and the critical need for thorough testing of device emulation components against malicious input scenarios.