CVE-2017-5956 in virglrenderer
Summary
by MITRE
The vrend_draw_vbo function in virglrenderer before 0.6.0 allows local guest OS users to cause a denial of service (out-of-bounds array access and QEMU process crash) via vectors involving vertext_buffer_index.
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Analysis
by VulDB Data Team • 09/10/2020
The vulnerability identified as CVE-2017-5956 resides within the virglrenderer component, specifically in the vrend_draw_vbo function that governs vertex buffer operations in virtualized graphics environments. This flaw affects versions prior to 060 and represents a critical security issue that can be exploited by local users within guest operating systems to disrupt service availability. The vulnerability manifests through improper input validation mechanisms that fail to adequately check array bounds when processing vertex buffer indices, creating a scenario where malicious input can lead to memory corruption and system instability.
The technical exploitation of this vulnerability occurs when a local guest OS user manipulates the vertext_buffer_index parameter in graphics rendering operations. This parameter controls which vertex buffer is accessed during draw operations, and the lack of proper bounds checking allows an attacker to specify an index that exceeds the allocated array boundaries. When the vrend_draw_vbo function processes this invalid index, it attempts to access memory locations outside the intended buffer range, resulting in out-of-bounds array access. This memory corruption directly leads to unpredictable behavior including segmentation faults and process termination, ultimately causing the QEMU process to crash and rendering the virtualized graphics environment unavailable.
The operational impact of CVE-2017-5956 extends beyond simple denial of service to potentially compromise the entire virtualization infrastructure. Since QEMU serves as a foundational component in many virtualization deployments, a crash of the QEMU process can affect multiple virtual machines running on the same host system. This vulnerability particularly affects cloud environments and virtual desktop infrastructures where multiple guests share the same hypervisor resources. The local privilege escalation aspect means that even users with minimal system access can trigger system-wide disruptions, making this vulnerability particularly dangerous in multi-tenant environments. The flaw aligns with CWE-129, which describes improper validation of array indices, and represents a classic example of buffer overflow conditions that can be exploited to cause system instability.
Mitigation strategies for this vulnerability require immediate patching of virglrenderer components to version 0.6.0 or later, where proper bounds checking mechanisms have been implemented. System administrators should prioritize updating virtualization environments to ensure all guest operating systems have access to patched graphics drivers and virtualization components. Additional protective measures include implementing strict input validation at multiple layers of the virtualization stack, monitoring for anomalous vertex buffer operations, and deploying intrusion detection systems that can identify suspicious graphics rendering patterns. Organizations should also consider implementing network segmentation and access controls to limit local user privileges within virtual environments. The vulnerability demonstrates the importance of proper memory management and bounds checking in virtualized graphics subsystems, aligning with ATT&CK technique T1499 for disruption of services through resource exhaustion and system instability. Regular security assessments of virtualization components should include thorough testing of graphics rendering functions to identify similar boundary condition vulnerabilities that could be exploited by local users to compromise system availability.