CVE-2016-8667 in QEMU
Summary
by MITRE
The rc4030_write function in hw/dma/rc4030.c in QEMU (aka Quick Emulator) allows local guest OS administrators to cause a denial of service (divide-by-zero error and QEMU process crash) via a large interval timer reload value.
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Analysis
by VulDB Data Team • 09/29/2022
The CVE-2016-8667 vulnerability resides within the QEMU virtualization platform's hardware emulation component, specifically in the rc4030_write function located in hw/dma/rc4030.c. This flaw represents a critical denial of service vulnerability that can be exploited by local guest operating system administrators to crash the QEMU process through a divide-by-zero error. The vulnerability manifests when a malicious guest administrator manipulates timer reload values, particularly those that are exceptionally large, causing the emulator to encounter an arithmetic exception during its processing of these values. The rc4030.c file implements a timer controller for certain emulated hardware platforms, and the write function handles timer configuration parameters that are critical for system timing operations.
The technical exploitation of this vulnerability occurs through improper input validation within the rc4030_write function where it processes timer interval values without adequate bounds checking or overflow protection. When a guest administrator sets a large interval timer reload value, the function attempts to perform arithmetic operations that result in division by zero, causing an unhandled exception that terminates the QEMU process. This type of vulnerability falls under CWE-369, which specifically addresses the divide-by-zero error condition, and represents a classic case of improper input validation leading to process termination. The vulnerability is particularly concerning because it can be triggered by any local guest administrator with access to timer configuration interfaces, making it exploitable within the virtualized environment without requiring external network access or elevated privileges beyond those already granted to the guest OS.
The operational impact of CVE-2016-8667 extends beyond simple service disruption as it can lead to complete virtual machine crashes and potential data loss for guest operating systems. When the QEMU process terminates due to this divide-by-zero error, all running virtual machines managed by that emulator instance become unavailable, potentially affecting multiple users or services that depend on the virtualized infrastructure. The vulnerability also impacts the stability of virtualized environments by creating unpredictable service interruptions that can be difficult to diagnose and recover from, especially in production environments where virtual machines are expected to maintain continuous operation. From an attack perspective, this vulnerability aligns with ATT&CK technique T1499.004, which involves network disruption through resource exhaustion or process termination, though in this case the disruption occurs at the hypervisor level rather than network level.
Mitigation strategies for CVE-2016-8667 involve both immediate patching and operational hardening measures. The primary solution is to apply the official QEMU patch that introduces proper bounds checking and input validation within the rc4030_write function to prevent division by zero conditions when processing large timer interval values. Organizations should also implement monitoring systems to detect unusual timer configuration changes within virtual machines, as these may indicate attempted exploitation. Additionally, virtualization administrators should consider implementing guest OS privilege restrictions to limit the ability of local administrators to modify timer configurations, though this approach may impact legitimate system administration tasks. The vulnerability demonstrates the importance of robust input validation in virtualization platforms and highlights the need for comprehensive security testing of hardware emulation components within hypervisor software to prevent similar issues from arising in other parts of the virtualization stack.