CVE-2016-9101 in QEMU
Summary
by MITRE
Memory leak in hw/net/eepro100.c in QEMU (aka Quick Emulator) allows local guest OS administrators to cause a denial of service (memory consumption and QEMU process crash) by repeatedly unplugging an i8255x (PRO100) NIC device.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-9101 represents a critical memory management flaw within the QEMU virtualization platform that affects the eepro100 network interface controller implementation. This issue resides in the hw/net/eepro100.c file and specifically targets the i8255x (PRO100) NIC device emulation functionality. The vulnerability manifests when local guest operating system administrators repeatedly perform the operation of unplugging the i8255x NIC device, leading to a systematic accumulation of memory that cannot be properly released back to the system. This memory leak behavior directly impacts the host system's resource management and overall virtualization stability.
The technical root cause of this vulnerability stems from improper memory deallocation mechanisms within the network device emulation code. When the i8255x NIC device is unplugged from a virtual machine, the associated memory structures that were allocated for network packet processing and device state management are not correctly freed from the QEMU process memory space. This memory leak occurs repeatedly with each unplugging operation, causing progressive memory consumption that eventually leads to system resource exhaustion. The flaw demonstrates characteristics consistent with CWE-401, which addresses improper handling of memory allocation and deallocation, and represents a classic example of resource leak vulnerabilities in virtualization environments. The vulnerability operates at the hypervisor level where guest operating systems can influence host system behavior through carefully crafted device management operations.
The operational impact of this vulnerability extends beyond simple resource consumption to potentially destabilize entire virtualization environments. As the memory leak accumulates, the QEMU process gradually consumes increasing amounts of system memory, which can eventually cause the virtual machine to crash or become unresponsive. This creates a denial of service condition that affects not only the specific virtual machine experiencing the leak but can also impact other virtual machines running on the same host system. The vulnerability is particularly concerning in multi-tenant environments where malicious or compromised guest operating systems could systematically consume host resources, leading to cascading failures and service disruption. From an attack perspective, this vulnerability aligns with ATT&CK technique T1499.001 which covers resource exhaustion attacks, and represents a form of hypervisor abuse where guest privileges are leveraged to affect host system stability.
Mitigation strategies for this vulnerability require immediate patch application from QEMU maintainers, as the issue affects core virtualization functionality. System administrators should implement monitoring solutions to detect unusual memory consumption patterns in QEMU processes and establish automated alerting for memory leak conditions. Virtualization administrators should consider implementing resource limits and quotas for QEMU processes to prevent single virtual machines from consuming excessive host resources. Additionally, guest operating system access controls should be tightened to limit the ability of local administrators to perform device unplugging operations, although this approach provides only partial protection. The vulnerability highlights the importance of proper memory management in virtualization environments and underscores the need for comprehensive testing of device emulation code to prevent similar resource leak conditions that could affect other virtualized hardware components.