CVE-2016-7170 in QEMU
Summary
by MITRE
The vmsvga_fifo_run function in hw/display/vmware_vga.c in QEMU (aka Quick Emulator) allows local guest OS administrators to cause a denial of service (out-of-bounds write and QEMU process crash) via vectors related to cursor.mask[] and cursor.image[] array sizes when processing a DEFINE_CURSOR svga command.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-7170 resides within the VMware VGA display driver implementation in QEMU, specifically within the vmsvga_fifo_run function located in hw/display/vmware_vga.c. This flaw represents a critical security issue that demonstrates how improper input validation can lead to severe system instability and denial of service conditions. The vulnerability manifests when processing DEFINE_CURSOR svga commands, which are used to configure cursor properties in virtualized graphics environments. The root cause stems from insufficient boundary checking on array access operations, creating opportunities for malicious actors to exploit memory corruption vulnerabilities through crafted cursor data.
The technical exploitation of this vulnerability occurs when a local guest OS administrator submits malicious cursor data that exceeds the predefined array boundaries for cursor.mask[] and cursor.image[] arrays. This improper validation allows an out-of-bounds write condition to occur, where the guest operating system can overwrite adjacent memory locations beyond the intended array boundaries. The vulnerability specifically targets the graphics processing pipeline within QEMU's virtualized display subsystem, where cursor configuration commands are interpreted and executed. When the malicious cursor data is processed, the lack of proper bounds checking on the array sizes leads to memory corruption that ultimately results in a complete crash of the QEMU process, rendering the virtual machine inaccessible and causing service disruption.
From an operational impact perspective, this vulnerability presents a significant risk to virtualized environments where guest operating systems have administrative privileges. The local privilege escalation aspect means that any user with administrative access within the guest can potentially trigger this denial of service condition, making it particularly dangerous in multi-tenant cloud environments or shared virtualization platforms. The vulnerability affects the availability of virtual machines and can be exploited to disrupt services without requiring external network access or elevated privileges beyond what is already available within the guest operating system. The crash behavior impacts not only individual virtual machines but can also affect the stability of the entire hypervisor environment, potentially causing cascading failures in larger virtualized infrastructures.
The vulnerability maps directly to CWE-121, which describes heap-based buffer overflow conditions, and CWE-787, which covers out-of-bounds write vulnerabilities. From an ATT&CK framework perspective, this vulnerability aligns with T1499.004, which covers network denial of service attacks, and T1068, which involves exploit for privilege escalation. The remediation strategy involves implementing proper input validation and bounds checking within the vmsvga_fifo_run function to ensure that cursor.mask[] and cursor.image[] array accesses remain within their defined boundaries. Additionally, the QEMU project should implement comprehensive memory safety checks and utilize static analysis tools to identify similar patterns throughout the codebase. The fix requires modification of the cursor data processing logic to validate array sizes before memory operations and to implement proper error handling that prevents out-of-bounds memory access conditions. Organizations should also consider implementing virtual machine isolation measures and monitoring for unusual cursor configuration patterns that might indicate exploitation attempts.