CVE-2017-9374 in QEMU
Summary
by MITRE
Memory leak in QEMU (aka Quick Emulator), when built with USB EHCI Emulation support, allows local guest OS privileged users to cause a denial of service (memory consumption) by repeatedly hot-unplugging the device.
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Analysis
by VulDB Data Team • 12/08/2022
The vulnerability identified as CVE-2017-9374 represents a critical memory management flaw within QEMU's USB EHCI (Enhanced Host Controller Interface) emulation subsystem. This issue manifests when QEMU is compiled with USB EHCI support enabled, creating a condition where guest operating systems with privileged access can exploit a memory leak through repeated hot-unplugging operations of USB devices. The flaw resides in the improper handling of memory allocation and deallocation within the USB controller emulation layer, specifically affecting how the emulator manages resources during device removal operations.
The technical implementation of this vulnerability stems from inadequate memory cleanup procedures within QEMU's USB EHCI implementation. When a USB device is hot-unplugged from a guest system, the emulator should properly release all associated memory structures and resources. However, the flaw causes the emulator to retain memory references or fail to properly deallocate memory blocks, leading to progressive memory consumption over time. This memory leak occurs repeatedly with each hot-unplug operation, allowing an attacker within the guest environment to systematically consume host system memory resources. The vulnerability is particularly concerning because it requires only local privileged access within the guest OS, making it exploitable by users with standard user privileges who can perform device management operations.
The operational impact of CVE-2017-9374 extends beyond simple resource exhaustion, as it can severely compromise system stability and availability. In virtualized environments, this vulnerability enables a denial of service attack that can gradually consume all available memory on the host system, potentially causing system crashes, performance degradation, or complete system unresponsiveness. The memory leak affects not only the specific QEMU instance but can also impact other virtual machines running on the same host, creating cascading effects in multi-tenant environments. Attackers can leverage this vulnerability to disrupt services, cause system instability, or perform resource exhaustion attacks against virtualized infrastructure. The flaw is particularly dangerous in cloud computing environments where multiple virtual machines share host resources, as a single compromised guest could potentially affect the entire host system's memory availability.
Mitigation strategies for CVE-2017-9374 should focus on both immediate remediation and long-term architectural improvements. The most effective immediate solution involves applying the official QEMU security patches released by the project maintainers, which address the specific memory leak in the USB EHCI emulation code. Organizations should also consider disabling USB EHCI emulation support in QEMU configurations when it is not required for specific use cases, reducing the attack surface. Additionally, implementing memory monitoring and alerting systems can help detect unusual memory consumption patterns that might indicate exploitation attempts. From a defensive standpoint, the vulnerability aligns with CWE-401, which categorizes improper resource management and memory leaks, while also mapping to ATT&CK technique T1499.001 for resource exhaustion attacks. Regular security assessments of virtualization environments, including vulnerability scanning of QEMU installations and monitoring of guest OS privileges, should be implemented to prevent exploitation. Network segmentation and limiting guest OS capabilities can also reduce the potential impact of such vulnerabilities by restricting the ability of compromised guests to perform device management operations that could trigger the memory leak condition.