CVE-2016-10155 in QEMU
Summary
by MITRE
Memory leak in hw/watchdog/wdt_i6300esb.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-2016-10155 resides within the QEMU virtualization platform's watchdog timer implementation, specifically in the hw/watchdog/wdt_i6300esb.c file. This memory leak affects the i6300esb watchdog device model that emulates the Intel 6300ESB watchdog timer hardware. The issue manifests when local guest operating system users with privileged access perform a large number of device unplug operations, creating a condition where allocated memory is not properly freed, leading to progressive memory consumption on the host system.
The technical flaw stems from improper memory management within the watchdog device's unplugging mechanism. When a guest OS user initiates device unplug operations, the code fails to properly release previously allocated memory structures associated with the watchdog timer state. This memory leak occurs repeatedly with each unplug operation, causing the QEMU process to consume increasing amounts of host memory until system resources are exhausted. The vulnerability is particularly concerning because it requires only local guest privileges to exploit, making it accessible to any user with access to the virtual machine.
From an operational impact perspective, this vulnerability enables a local privilege escalation attack that results in a denial of service condition affecting the entire host system. The progressive memory consumption eventually leads to host memory exhaustion, causing the QEMU process to crash and terminate the virtual machine. This disruption affects not only the targeted virtual machine but can also impact other virtual machines running on the same host, potentially causing cascading failures in virtualized environments. The vulnerability represents a classic case of resource exhaustion that undermines system stability and availability.
The flaw aligns with CWE-401, which describes improper cleanup of dynamically allocated memory, and can be mapped to ATT&CK technique T1499.001 for resource exhaustion attacks. Organizations running virtualized environments are particularly vulnerable as this attack can be executed from within any guest OS with sufficient privileges, making it a significant concern for cloud providers and enterprise virtualization deployments. The vulnerability demonstrates the critical importance of proper memory management in virtualization software and highlights the potential for guest-to-host privilege escalation through memory management flaws.
Mitigation strategies should include applying the latest QEMU patches that address the memory leak in the watchdog device implementation. System administrators should also implement monitoring for unusual memory consumption patterns in QEMU processes and consider implementing resource limits on virtual machine processes to prevent complete system exhaustion. Additionally, guest OS privilege management should be strictly enforced to limit the ability of untrusted users to perform device unplug operations. Regular security audits of virtualization components and keeping all hypervisor software up to date remain essential practices for preventing exploitation of similar memory management vulnerabilities.