CVE-2017-5857 in QEMU
Summary
by MITRE
Memory leak in the virgl_cmd_resource_unref function in hw/display/virtio-gpu-3d.c in QEMU (aka Quick Emulator) allows local guest OS users to cause a denial of service (host memory consumption) via a large number of VIRTIO_GPU_CMD_RESOURCE_UNREF commands sent without detaching the backing storage beforehand.
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Analysis
by VulDB Data Team • 09/09/2020
The vulnerability identified as CVE-2017-5857 represents a critical memory management flaw within the QEMU virtualization environment that specifically targets the virtio-gpu-3d component. This issue manifests in the virgl_cmd_resource_unref function located in the hw/display/virtio-gpu-3d.c file, where improper handling of GPU resource references creates a persistent memory leak condition. The vulnerability is particularly concerning because it operates within the guest operating system context, allowing malicious local users to exploit the flaw without requiring elevated privileges or external network access. The root cause stems from the failure to properly clean up memory resources when the VIRTIO_GPU_CMD_RESOURCE_UNREF command is executed without first detaching the backing storage, creating a scenario where allocated memory remains unreleased even after the resource reference count reaches zero.
The technical implementation of this vulnerability leverages the virtio-gpu subsystem's resource management mechanisms to repeatedly send resource unreference commands without the necessary preconditions for proper cleanup. When a guest OS user executes a large number of these commands in succession, the system accumulates unreleased memory blocks that persist in the host's memory space, gradually consuming available resources. This memory leak directly violates the fundamental principles of resource management and can be classified under CWE-401 as "Improper Release of Memory Before Removing Last Reference" and aligns with ATT&CK technique T1499.001 for "Network Denial of Service" through resource exhaustion. The flaw demonstrates a classic case of insufficient validation of command parameters and resource state transitions within the virtual GPU implementation, where the system fails to verify that backing storage has been properly detached before proceeding with resource cleanup operations.
The operational impact of CVE-2017-5857 extends beyond simple resource consumption to potentially destabilize entire virtualized environments and compromise system availability. Host systems running QEMU with virtio-gpu enabled become increasingly vulnerable to memory exhaustion attacks as the cumulative effect of leaked memory blocks grows with repeated exploitation attempts. This vulnerability affects organizations relying on virtualized infrastructure where guest operating systems may be compromised or where untrusted users have access to virtual machines. The memory consumption pattern creates a gradual degradation of system performance that may not be immediately apparent but eventually leads to complete denial of service conditions. Security professionals should recognize this as a potential indicator of privilege escalation attempts or insider threats, as attackers can leverage this flaw to systematically consume host resources and potentially cause cascading failures in virtualized environments. The vulnerability also impacts compliance with security standards requiring proper resource management and memory safety protocols.
Mitigation strategies for CVE-2017-5857 require both immediate and long-term approaches to address the underlying memory management issues. System administrators should implement strict resource limits and monitoring for memory consumption on hosts running QEMU virtual machines, particularly those with virtio-gpu enabled. The most effective immediate solution involves applying the vendor-provided patches that correct the resource unreference logic in the virtio-gpu subsystem, ensuring proper detachment of backing storage before resource cleanup operations. Organizations should also consider implementing guest isolation measures and limiting the ability of guest operating systems to send excessive GPU commands, while establishing robust monitoring for unusual memory consumption patterns. The fix addresses the core issue by enforcing proper resource state validation and ensuring that all memory allocated for GPU resources is properly released regardless of the command execution sequence. Security teams should also conduct regular vulnerability assessments of virtualization components and maintain updated threat intelligence regarding similar memory management flaws in hypervisor implementations. This vulnerability underscores the importance of proper resource lifecycle management in virtualized environments and highlights the need for comprehensive security testing of virtual GPU implementations to prevent similar issues from emerging in other components of the virtualization stack.