CVE-2014-7815 in QEMU
Summary
by MITRE
The set_pixel_format function in ui/vnc.c in QEMU allows remote attackers to cause a denial of service (crash) via a small bytes_per_pixel value.
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Analysis
by VulDB Data Team • 02/24/2022
The vulnerability identified as CVE-2014-7815 resides within the QEMU virtualization platform's VNC implementation, specifically in the set_pixel_format function located in ui/vnc.c. This flaw represents a classic buffer manipulation issue that can be exploited by remote attackers to disrupt the normal operation of virtual machine instances. The vulnerability occurs when the VNC server processes pixel format requests from remote clients, creating a scenario where malformed data can trigger unexpected behavior in the underlying graphics handling code. The issue is particularly concerning because it affects the core virtualization infrastructure that many organizations rely upon for computing resources and network services.
The technical exploitation of this vulnerability stems from insufficient input validation within the set_pixel_format function, which fails to properly validate the bytes_per_pixel parameter provided by remote VNC clients. When an attacker sends a maliciously crafted bytes_per_pixel value that is unusually small, the function does not adequately check the validity of this parameter before proceeding with pixel format processing. This lack of validation creates a condition where the function attempts to operate on invalid memory boundaries or perform calculations that result in memory corruption. The vulnerability is categorized under CWE-129 as an insufficient input validation issue, where the system fails to properly validate the range or size of input parameters before processing them. The specific nature of the flaw allows for a controlled crash condition that can be reliably reproduced by sending malformed VNC protocol messages.
The operational impact of CVE-2014-7815 extends beyond simple service disruption, as it can be leveraged to create persistent denial of service conditions that may affect virtualized environments critical to enterprise operations. In cloud computing deployments and data center environments where QEMU serves as the underlying virtualization engine, this vulnerability can be exploited to crash virtual machine instances without requiring authentication or elevated privileges. The attack surface is particularly broad since VNC services are commonly exposed to untrusted networks for remote administration purposes, making the vulnerability accessible to attackers with minimal network access. From an attack framework perspective, this vulnerability aligns with ATT&CK technique T1499.004 for network denial of service, where adversaries can disrupt services by exploiting implementation flaws in system components. The vulnerability affects virtualization platforms that utilize QEMU's VNC server functionality, potentially impacting organizations running virtualized workloads across various infrastructure types.
Mitigation strategies for CVE-2014-7815 should focus on both immediate patching and operational security measures to reduce exposure. The primary remediation involves applying the official QEMU patch that was released to address the input validation flaw in the set_pixel_format function, ensuring that bytes_per_pixel values are properly validated before processing. Organizations should also implement network segmentation to limit access to VNC services, particularly ensuring that VNC ports are not exposed to untrusted networks without proper authentication mechanisms. Network-based mitigations can include implementing firewall rules that restrict VNC access to trusted IP ranges and deploying intrusion detection systems to monitor for suspicious VNC protocol traffic patterns. Additionally, administrators should consider disabling VNC services when they are not actively needed and implementing proper access controls through SSH tunneling or VPN connections to provide secure remote access to virtual machine console sessions. The vulnerability serves as a reminder of the importance of validating all external inputs in virtualization platforms, as these systems often serve as critical infrastructure components that require robust security measures to prevent exploitation.