CVE-2016-7994 in QEMU
Summary
by MITRE
Memory leak in the virtio_gpu_resource_create_2d function in hw/display/virtio-gpu.c in QEMU (aka Quick Emulator) allows local guest OS administrators to cause a denial of service (memory consumption) via a large number of VIRTIO_GPU_CMD_RESOURCE_CREATE_2D commands.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-7994 represents a critical memory management flaw within the QEMU virtualization platform that specifically affects the virtio-gpu subsystem. This issue manifests in the hw/display/virtio-gpu.c file where the virtio_gpu_resource_create_2d function fails to properly handle memory allocation for graphics resources, creating a persistent memory leak condition. The vulnerability operates at the hypervisor level and specifically targets the virtual graphics processing unit implementation that enables guest operating systems to communicate with virtualized display hardware. This flaw is particularly concerning because it allows local administrators within the guest operating system to exploit the memory leak through repeated invocation of VIRTIO_GPU_CMD_RESOURCE_CREATE_2D commands, which are standard graphics resource allocation requests used by virtualized graphics environments. The root cause of this vulnerability aligns with CWE-401, which catalogs improper resource management issues where allocated memory is not properly freed, leading to resource exhaustion. The attack vector is significant as it requires only local administrative privileges within the guest OS, making it accessible to any user with sufficient privileges to execute the specific command sequence. From an operational perspective, this vulnerability can be classified under ATT&CK technique T1499.003, which covers resource exhaustion attacks targeting virtualization platforms. The memory leak occurs because each successful VIRTIO_GPU_CMD_RESOURCE_CREATE_2D command creates a new graphics resource allocation without properly cleaning up previous allocations, resulting in gradual memory consumption that can eventually exhaust the host system's available memory resources. This type of vulnerability undermines the fundamental security principle of resource isolation in virtualized environments, where guest operating systems should be contained and unable to impact the stability of the host system or other guests. The impact extends beyond simple denial of service, as memory exhaustion on the host can lead to system instability, performance degradation, and potentially compromise the integrity of other virtual machines running on the same physical host. The vulnerability affects QEMU versions prior to 2.7.0 and represents a classic case of inadequate memory management in virtualized graphics subsystems where the lack of proper resource cleanup mechanisms allows for progressive resource consumption. The flaw demonstrates the critical importance of robust memory management practices in hypervisor components, particularly in graphics virtualization where resource allocation patterns can be easily manipulated by malicious or compromised guest users. Effective mitigation strategies include applying the official QEMU patch released in version 2.7.0, which implements proper resource cleanup for graphics allocations, as well as implementing monitoring systems that can detect unusual memory consumption patterns in virtualized environments. Additionally, administrators should consider implementing resource limits and quotas on virtual machines to prevent single guests from consuming excessive memory resources, and should regularly audit their virtualization environments for similar memory management issues in other subsystems. The vulnerability underscores the necessity of comprehensive security testing for virtualization components, particularly those handling user input and resource allocation requests, and highlights the importance of maintaining up-to-date virtualization platforms to protect against known memory management flaws that can be exploited for denial of service attacks.