CVE-2016-4453 in QEMU
Summary
by MITRE
The vmsvga_fifo_run function in hw/display/vmware_vga.c in QEMU allows local OS guest administrators to cause a denial of service (infinite loop and QEMU process crash) via a VGA command.
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Analysis
by VulDB Data Team • 08/22/2022
The vulnerability identified as CVE-2016-4453 resides within the VMware VGA display driver implementation in QEMU virtualization software, specifically in the vmsvga_fifo_run function located in hw/display/vmware_vga.c. This flaw represents a critical security issue that affects virtualized environments where QEMU serves as the hypervisor platform. The vulnerability manifests when local administrators within a guest operating system execute malicious VGA commands that trigger an infinite loop condition within the virtual graphics subsystem. The affected code path processes VGA command FIFO (First In, First Out) operations, which are fundamental to handling graphics operations in virtualized display environments. When properly crafted VGA commands are submitted through the FIFO mechanism, the function fails to properly validate command parameters, leading to a condition where the processing loop becomes indefinitely trapped.
The technical exploitation of this vulnerability occurs through the manipulation of VGA command sequences that are processed by the vmsvga_fifo_run function. This function operates within the context of virtual graphics hardware emulation, where it handles commands from guest operating systems to manage display operations. The flaw stems from inadequate input validation and boundary checking within the FIFO processing logic, allowing malicious command sequences to cause the function to enter an infinite loop. The loop occurs because the function does not properly handle certain command structures that result in self-referential or circular processing conditions. When this infinite loop is triggered, it consumes all available CPU resources within the QEMU process, effectively causing a denial of service condition that crashes the entire QEMU virtual machine process. This represents a classic example of a resource exhaustion attack that can be executed by any local administrator within the guest system.
The operational impact of CVE-2016-4453 extends beyond simple denial of service, as it can be leveraged to disrupt critical virtualized services and applications running within QEMU environments. In enterprise virtualization deployments, this vulnerability allows unauthorized local users within guest operating systems to crash the host QEMU processes, potentially affecting multiple virtual machines running on the same physical host. The vulnerability is particularly concerning because it requires minimal privileges for exploitation, as local administrators typically have sufficient access to manipulate VGA commands within their guest environments. This makes the attack vector highly accessible and potentially devastating in multi-tenant virtualization environments where guest isolation is critical. The vulnerability aligns with CWE-835, which describes the weakness of infinite loops, and can be categorized under the ATT&CK technique T1499.004 for Network Denial of Service, as the impact extends to networked virtualized environments where service availability is paramount.
Mitigation strategies for this vulnerability require immediate patching of QEMU installations to address the flawed FIFO processing logic in the VMware VGA driver. System administrators should prioritize updating QEMU to versions that contain fixes for this specific vulnerability, as the patch typically involves implementing proper input validation and boundary checks within the vmsvga_fifo_run function. Additionally, implementing proper command filtering and validation at the guest operating system level can help prevent malicious VGA command sequences from reaching the vulnerable code path. Network segmentation and virtual machine isolation measures can also reduce the potential impact of exploitation, though these are secondary mitigations. Organizations should also consider implementing monitoring solutions that can detect anomalous CPU usage patterns that might indicate exploitation attempts, as the infinite loop condition creates distinctive performance signatures that can be monitored for suspicious activity. The vulnerability demonstrates the importance of thorough input validation in virtualization components, particularly those handling graphics and display operations that interface between guest and host systems.