CVE-2017-5525 in QEMU
Summary
by MITRE
Memory leak in hw/audio/ac97.c in QEMU (aka Quick Emulator) allows local guest OS privileged users to cause a denial of service (host memory consumption and QEMU process crash) via a large number of device unplug operations.
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Analysis
by VulDB Data Team • 09/08/2020
The vulnerability identified as CVE-2017-5525 represents a critical memory management flaw within the QEMU virtualization platform that affects the AC97 audio device emulation component. This issue resides in the hw/audio/ac97.c file where improper memory deallocation occurs during device unplug operations, creating a persistent memory leak condition that can be exploited by malicious actors within the guest operating system. The flaw specifically manifests when privileged users within the guest environment perform repeated device unplug operations, leading to progressive host memory exhaustion and eventual system instability.
The technical root cause of this vulnerability stems from inadequate memory cleanup procedures within the AC97 audio controller implementation. When guest operating systems repeatedly issue device unplug commands to the emulated AC97 audio device, the QEMU emulator fails to properly release allocated memory structures back to the host system. This memory leak occurs because the code does not adequately track and free memory blocks associated with audio device instances during the unplug sequence. The vulnerability is classified under CWE-401 as a failure to release memory resources, making it a classic example of resource exhaustion through improper memory management. The flaw is particularly concerning because it requires only local privileged access within the guest OS to exploit, making it accessible to any user with sufficient privileges to manipulate audio device operations.
The operational impact of this vulnerability extends beyond simple resource consumption to encompass complete system availability compromise. As the memory leak accumulates through repeated unplug operations, host system memory becomes progressively consumed until the QEMU process either crashes or becomes unresponsive due to memory exhaustion. This creates a reliable denial of service condition that can be used to disrupt virtualized environments and compromise the stability of the entire virtualization infrastructure. Attackers can leverage this vulnerability to systematically consume host resources and potentially cause cascading failures in multi-tenant virtualization environments where multiple guest VMs share the same physical host resources. The vulnerability affects all versions of QEMU that implement the AC97 audio device emulation and impacts any system where virtual machines utilize audio functionality, making it particularly dangerous in cloud computing and enterprise virtualization deployments.
Mitigation strategies for CVE-2017-5525 should focus on both immediate patching and operational hardening measures. The primary solution involves applying the official QEMU patch that addresses the memory leak in the audio device cleanup routine, ensuring proper memory deallocation occurs during device unplug operations. Organizations should also implement monitoring solutions to detect unusual patterns of audio device manipulation that could indicate exploitation attempts. Additionally, system administrators should consider limiting guest OS privileges for audio device operations and implementing resource limits on QEMU processes to prevent complete system exhaustion. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving resource exhaustion and denial of service, making it a critical concern for defensive security operations. The vulnerability demonstrates the importance of proper memory management in virtualization platforms and highlights the need for comprehensive testing of device emulation components under stress conditions to prevent similar issues in other virtualization subsystems.