CVE-2016-4454 in QEMU
Summary
by MITRE
The vmsvga_fifo_read_raw function in hw/display/vmware_vga.c in QEMU allows local OS guest administrators to obtain sensitive host memory information or cause a denial of service (QEMU process crash) by changing FIFO registers and issuing a VGA command, which triggers an out-of-bounds read.
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Analysis
by VulDB Data Team • 08/22/2022
The vulnerability identified as CVE-2016-4454 resides within the VMware VGA display driver implementation in QEMU virtualization software, specifically in the vmsvga_fifo_read_raw 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 attempt to manipulate FIFO registers and subsequently issue VGA commands, creating conditions that lead to unauthorized memory access patterns.
The technical exploitation of this vulnerability stems from inadequate bounds checking within the vmsvga_fifo_read_raw function, which processes raw FIFO data reads for VMware VGA hardware emulation. When an authenticated guest administrator modifies FIFO registers and executes VGA commands, the function fails to validate the boundaries of memory access operations, resulting in out-of-bounds read conditions. This memory access violation occurs because the implementation does not properly validate the size or range of data being accessed from the FIFO buffer, allowing malicious input to traverse beyond intended memory boundaries.
The operational impact of CVE-2016-4454 extends beyond simple denial of service scenarios to include potential information disclosure risks. Local guest administrators can leverage this vulnerability to extract sensitive host memory information, potentially accessing data that should remain isolated within the hypervisor environment. This information disclosure capability poses significant risks to virtualized infrastructure security, as it enables attackers to gather confidential data that may include system configuration details, memory contents, or other sensitive information. Additionally, the vulnerability can trigger QEMU process crashes, leading to denial of service conditions that disrupt virtual machine operations and potentially affecting multiple guest instances running on the same host.
From a cybersecurity perspective, this vulnerability aligns with CWE-129, which addresses improper validation of array index values, and represents a classic example of an out-of-bounds read condition. The ATT&CK framework categorizes this vulnerability under privilege escalation and defense evasion techniques, as local guest administrators can leverage it to gain unauthorized access to host resources while potentially avoiding detection mechanisms. The vulnerability's exploitation requires local administrative privileges within the guest operating system, making it a privilege escalation vector rather than a direct remote attack surface, though it still represents a significant risk to virtualized environments.
Mitigation strategies for CVE-2016-4454 should focus on immediate patching of QEMU installations to address the bounds checking deficiencies in the VMware VGA driver implementation. System administrators should also implement network segmentation and access controls to limit guest administrator privileges where possible, reducing the attack surface for potential exploitation. Additional defensive measures include monitoring for unusual VGA command sequences and FIFO register modifications, as well as implementing hypervisor-level security controls that can detect and prevent unauthorized memory access patterns. Organizations should also consider virtual machine isolation techniques and regular security assessments of their virtualized environments to identify and remediate similar vulnerabilities in other hypervisor components.