CVE-2017-5937 in virglrenderer
Summary
by MITRE
The util_format_is_pure_uint function in vrend_renderer.c in Virgil 3d project (aka virglrenderer) 0.6.0 and earlier allows local guest OS users to cause a denial of service (NULL pointer dereference) via a crafted VIRGL_CCMD_CLEAR command.
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Analysis
by VulDB Data Team • 09/08/2020
The vulnerability identified as CVE-2017-5937 resides within the Virgil 3D project, specifically in the virglrenderer component version 0.6.0 and earlier. This issue manifests as a NULL pointer dereference that can be exploited by local guest OS users to trigger a denial of service condition. The affected function, util_format_is_pure_uint, is part of the vrend_renderer.c file which handles rendering operations for virtualized graphics environments. The vulnerability occurs when processing a crafted VIRGL_CCMD_CLEAR command, which is a specific command used in the virtual graphics rendering pipeline to clear framebuffer contents. This type of vulnerability represents a critical security flaw in virtualized graphics environments where guest operating systems interact with host graphics drivers through virtualization layers.
The technical flaw stems from insufficient input validation within the util_format_is_pure_uint function which fails to properly handle null pointer references when processing the VIRGL_CCMD_CLEAR command. When a malicious guest OS user sends a specially crafted command sequence, the function attempts to dereference a pointer that has not been properly initialized or validated, leading to a segmentation fault and subsequent system crash. This behavior aligns with CWE-476, which describes NULL pointer dereference vulnerabilities that occur when a null value is used as a pointer reference. The vulnerability specifically exploits the lack of proper parameter validation in the graphics command processing pipeline, where the renderer does not adequately verify the integrity of incoming commands before attempting to process them.
The operational impact of this vulnerability extends beyond simple denial of service, as it can severely disrupt virtualized graphics environments where multiple guest operating systems share the same host resources. Local guest OS users who can execute code within their virtual machines gain the ability to crash the graphics rendering subsystem, potentially affecting other virtual machines running on the same host. This vulnerability is particularly concerning in cloud computing environments and virtual desktop infrastructures where multiple users share the same physical hardware. The exploitation can lead to complete service disruption for graphics-intensive applications, forcing administrators to restart virtual machines or even entire host systems. From an attacker perspective, this represents a low-effort method to cause system instability, with potential for escalation if combined with other vulnerabilities in the virtualization stack.
Mitigation strategies for CVE-2017-5937 should focus on immediate patching of the virglrenderer component to version 0.6.1 or later where the NULL pointer dereference has been addressed. System administrators should implement strict input validation policies for all graphics command processing, ensuring that all incoming commands are properly validated before execution. The vulnerability can be addressed through defensive programming practices that include null pointer checks and proper error handling within the util_format_is_pure_uint function. Additionally, implementing monitoring and alerting mechanisms for unusual graphics command patterns can help detect potential exploitation attempts. Organizations should also consider isolating graphics-intensive virtual machines and implementing network segmentation to limit the potential impact of such vulnerabilities. The remediation process should include comprehensive testing to ensure that patched systems maintain proper graphics functionality while eliminating the vulnerability. This vulnerability demonstrates the importance of proper input validation in virtualized environments and aligns with ATT&CK technique T1059.007 for command and scripting interpreter, where local users can leverage system vulnerabilities to execute malicious commands that trigger system instability.