CVE-2016-8669 in QEMU
Summary
by MITRE
The serial_update_parameters function in hw/char/serial.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 vectors involving a value of divider greater than baud base.
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Analysis
by VulDB Data Team • 09/29/2022
The vulnerability identified as CVE-2016-8669 resides within the QEMU virtual machine emulator's serial port implementation, specifically in the serial_update_parameters function located in the hw/char/serial.c source file. This flaw represents a critical security issue that can be exploited by local administrators within a guest operating system to disrupt the host virtualization environment. The vulnerability manifests when malicious input is provided to the serial port parameter handling mechanism, creating a scenario where a divide-by-zero error occurs during the processing of serial communication parameters.
The technical exploitation of this vulnerability occurs through manipulation of the divider parameter in serial port configuration, where values exceeding the baud base threshold trigger an arithmetic exception. When the serial_update_parameters function processes a divider value that surpasses the established baud base limit, the code fails to properly validate this input before performing division operations. This validation failure results in a mathematical division by zero, which causes the QEMU process to terminate abruptly and crash. The flaw stems from inadequate input sanitization and boundary checking within the serial communication subsystem, allowing malformed parameter values to propagate through the system without proper error handling.
The operational impact of CVE-2016-8669 extends beyond simple denial of service, as it can be leveraged to disrupt virtualized environments that rely on QEMU for guest machine management. Local guest administrators who gain sufficient privileges can exploit this vulnerability to crash the QEMU process, effectively terminating the virtual machine session and potentially causing data loss or service interruption. This vulnerability particularly affects systems where guest operating systems have administrative access and can manipulate serial port parameters, which is common in many virtualized environments where console access and serial communication are utilized for debugging, monitoring, or system administration purposes. The attack vector is particularly concerning because it requires minimal privileges and can be executed from within the guest environment, making it a significant threat to virtual machine isolation and system stability.
Mitigation strategies for CVE-2016-8669 involve immediate patching of QEMU installations to address the divide-by-zero condition in the serial parameter handling code. System administrators should ensure that all QEMU instances are updated to versions that include proper input validation and boundary checking for serial port parameters. Additionally, implementing network segmentation and access controls can limit the potential impact of such vulnerabilities by restricting guest administrator privileges and reducing the attack surface. The vulnerability aligns with CWE-369, which describes the weakness of division by zero, and can be categorized under ATT&CK technique T1499.001 for network denial of service attacks. Organizations should also consider implementing monitoring solutions that can detect anomalous serial port parameter changes and process termination events that may indicate exploitation attempts. Regular security assessments of virtualization environments are essential to identify and remediate similar vulnerabilities in other components of the virtual machine infrastructure.