CVE-2016-2198 in QEMU
Summary
by MITRE
QEMU (aka Quick Emulator) built with the USB EHCI emulation support is vulnerable to a null pointer dereference flaw. It could occur when an application attempts to write to EHCI capabilities registers. A privileged user inside quest could use this flaw to crash the QEMU process instance resulting in DoS.
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Analysis
by VulDB Data Team • 10/13/2022
The vulnerability identified as CVE-2016-2198 affects QEMU, a widely used open-source emulator that allows users to run multiple operating systems on a single machine. This issue specifically targets QEMU configurations that include USB EHCI (Enhanced Host Controller Interface) emulation capabilities, which are essential for supporting modern USB 2.0 devices within virtualized environments. The flaw manifests as a null pointer dereference condition that occurs during specific interactions with USB EHCI capabilities registers, representing a critical security weakness in virtualization infrastructure.
The technical implementation of this vulnerability stems from improper validation of pointer references within QEMU's USB EHCI emulation code. When a privileged guest operating system user attempts to write to EHCI capabilities registers, the emulator fails to properly check whether certain pointers are null before dereferencing them. This fundamental flaw in input validation creates an exploitable condition where malicious code within the guest environment can trigger a segmentation fault or crash within the QEMU process. The vulnerability is particularly concerning because it requires only a privileged user context within the guest operating system, making it accessible to attackers who have already gained some level of access to the virtual machine.
The operational impact of CVE-2016-2198 extends beyond simple denial-of-service conditions, as it represents a potential pathway for privilege escalation and system compromise within virtualized environments. A malicious user with access to a guest operating system could leverage this vulnerability to crash the QEMU process, potentially causing the entire virtual machine to become unresponsive or requiring manual intervention to restart the virtualization instance. This disruption affects not only the individual virtual machine but can also impact the broader virtualization infrastructure, especially in cloud computing environments where multiple VMs share the same host resources. The vulnerability aligns with CWE-476, which categorizes null pointer dereference flaws as a fundamental weakness in software design that can lead to system instability and potential security breaches.
From a threat modeling perspective, this vulnerability demonstrates the inherent risks associated with complex virtualization software that must accurately emulate hardware behaviors while maintaining system security boundaries. The attack vector requires a privileged user within the guest system, which aligns with ATT&CK technique T1059 for command and control operations and T1499 for endpoint denial of service. Organizations using QEMU for virtualization must consider the implications of this flaw in their security posture, particularly in multi-tenant environments where guest isolation is paramount. The vulnerability also highlights the importance of proper input validation and defensive programming practices in hypervisor and emulator software, as these components serve as critical infrastructure elements that must maintain stability even when subjected to malicious inputs from potentially compromised guest operating systems.
Mitigation strategies for CVE-2016-2198 should focus on both immediate remediation and long-term architectural improvements. The most effective immediate solution involves updating QEMU to versions that contain the patched implementation of USB EHCI emulation logic, which properly validates pointer references before dereferencing. Organizations should also consider implementing additional security measures such as disabling unnecessary USB emulation features when they are not required, employing network segmentation to limit guest access, and monitoring for unusual process termination patterns that might indicate exploitation attempts. The vulnerability serves as a reminder of the critical importance of maintaining up-to-date virtualization software and implementing proper security controls around privileged guest access. Regular vulnerability assessments and penetration testing of virtualization environments can help identify similar issues that might exist in other components of the virtual infrastructure, ensuring comprehensive protection against both known and emerging threats.