CVE-2017-9375 in QEMU
Summary
by MITRE
QEMU (aka Quick Emulator), when built with USB xHCI controller emulator support, allows local guest OS privileged users to cause a denial of service (infinite recursive call) via vectors involving control transfer descriptors sequencing.
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Analysis
by VulDB Data Team • 12/08/2022
The vulnerability identified as CVE-2017-9375 affects QEMU, a widely used open-source emulator that enables users to run multiple operating systems on a single physical machine. This issue specifically manifests when QEMU is compiled with USB xHCI (eXtensible Host Controller Interface) controller emulator support, which is essential for emulating modern USB 3.0 devices within virtualized environments. The flaw resides in how the emulator handles control transfer descriptors during USB communication sequences, creating a critical security gap that can be exploited by malicious actors within the guest operating system.
The technical implementation of this vulnerability involves a flaw in the USB xHCI controller emulation logic where specific sequences of control transfer descriptors can trigger an infinite recursive call within the emulator's processing code. When a privileged user within the guest operating system crafts malicious USB control transfer requests with particular descriptor arrangements, the emulator enters into an endless loop of recursive function calls that consumes excessive system resources and ultimately leads to a denial of service condition. This recursive behavior occurs because the emulator fails to properly validate or limit the depth of descriptor processing, allowing an attacker to manipulate the control flow in a way that prevents normal operation.
The operational impact of this vulnerability extends beyond simple service disruption as it represents a significant threat to virtualized environments where guest operating systems may have elevated privileges. Attackers with access to a guest OS, particularly those with user-level privileges that can interact with USB devices, can leverage this vulnerability to exhaust system resources and potentially crash the entire virtual machine or host system. The flaw is particularly concerning in enterprise environments where virtualization is extensively used, as it could be exploited to create persistent denial of service conditions that impact business operations and availability of critical services.
This vulnerability aligns with CWE-674, which describes "Uncontrolled Recursion" in software systems, where recursive functions lack proper termination conditions or depth limits. From an adversarial perspective, this issue maps to ATT&CK technique T1499.004, which involves network denial of service attacks through resource exhaustion, and T1059.001, covering command and scripting interpreter usage for system manipulation. The exploitability of this vulnerability requires the attacker to have access to the guest operating system with sufficient privileges to interact with USB devices, making it a medium-severity threat that can be leveraged in various attack scenarios.
Mitigation strategies for CVE-2017-9375 include updating QEMU to versions that contain patches addressing the recursive call handling in USB xHCI controller emulation, implementing proper input validation for USB descriptor sequences, and applying runtime limits on recursive function calls within the emulator. System administrators should also consider isolating USB device access within virtual machines, implementing network segmentation, and monitoring for unusual resource consumption patterns that might indicate exploitation attempts. Additionally, organizations should ensure that guest operating systems have appropriate privilege controls to limit the potential impact of compromised user accounts and maintain regular patch management processes to address similar vulnerabilities in virtualization software components.