CVE-2015-8568 in QEMU
Summary
by MITRE
Memory leak in QEMU, when built with a VMWARE VMXNET3 paravirtual NIC emulator support, allows local guest users to cause a denial of service (host memory consumption) by trying to activate the vmxnet3 device repeatedly.
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Analysis
by VulDB Data Team • 08/29/2020
The vulnerability identified as CVE-2015-8568 represents a critical memory management flaw within the QEMU virtualization platform that specifically manifests when the VMware VMXNET3 paravirtual Network Interface Card emulator is enabled. This issue stems from improper memory deallocation mechanisms within the virtual network device implementation, creating a condition where repeated attempts to activate the vmxnet3 device result in progressive memory consumption on the host system. The vulnerability affects systems running QEMU versions that include VMXNET3 support, making it particularly relevant to virtualized environments where this specific network adapter is utilized. The memory leak occurs during the device activation sequence, where allocated memory structures are not properly freed upon repeated initialization attempts, leading to gradual host resource exhaustion.
The technical root cause of this vulnerability aligns with CWE-401, which describes improper handling of memory allocation and deallocation, specifically manifesting as memory leaks in software systems. When a guest operating system attempts to activate the vmxnet3 device multiple times, the QEMU emulator fails to properly release previously allocated memory segments associated with the network interface. This memory management failure creates a cumulative effect where each activation attempt consumes additional host memory without corresponding release, eventually leading to system performance degradation or complete denial of service. The vulnerability operates at the hypervisor level, making it particularly dangerous as it can be exploited by unprivileged guest users who have access to the virtual machine's operating system.
From an operational perspective, this vulnerability presents a significant threat to virtualized environments where QEMU serves as the underlying virtualization platform. The denial of service condition can result in complete system unavailability, as host memory consumption continues to increase until system resources are exhausted. Attackers can exploit this vulnerability by simply repeatedly activating the vmxnet3 device from within the guest operating system, requiring minimal privileges and technical expertise. This makes the vulnerability particularly dangerous in multi-tenant environments or cloud computing scenarios where guest users may have limited privileges but could still cause substantial disruption to other virtual machines running on the same host. The impact extends beyond simple resource exhaustion, potentially affecting the stability of entire virtualized infrastructures and leading to cascading failures in complex virtual environments.
The mitigation strategies for CVE-2015-8568 should focus on both immediate remediation and long-term architectural improvements. The most effective immediate solution involves applying the vendor-provided patches that address the memory deallocation issues in the VMXNET3 emulator implementation. Organizations should also consider implementing resource limits and monitoring mechanisms to detect unusual memory consumption patterns that could indicate exploitation attempts. From a security architecture standpoint, this vulnerability highlights the importance of proper memory management in hypervisor components and aligns with ATT&CK technique T1499.001, which covers network denial of service attacks. Additionally, implementing network segmentation and access controls to limit guest user capabilities can reduce the attack surface, while regular vulnerability assessments and security audits should be conducted to identify similar memory management flaws in other virtualization components. The vulnerability serves as a reminder of the critical need for rigorous memory management practices in virtualization software, particularly in components that handle device initialization and resource allocation.