CVE-2017-5993 in virglrenderer
Summary
by MITRE
Memory leak in the vrend_renderer_init_blit_ctx function in vrend_blitter.c in virglrenderer before 0.6.0 allows local guest OS users to cause a denial of service (host memory consumption) via a large number of VIRGL_CCMD_BLIT commands.
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Analysis
by VulDB Data Team • 09/08/2020
The vulnerability described in CVE-2017-5993 represents a critical memory management flaw within the virglrenderer library, specifically affecting the vrend_renderer_init_blit_ctx function in the vrend_blitter.c component. This issue exists in versions prior to 0.6.0 and demonstrates a classic memory leak pattern that can be exploited by local guest operating system users to consume excessive host memory resources. The vulnerability manifests when a large number of VIRGL_CCMD_BLIT commands are processed, leading to uncontrolled memory growth on the host system. This memory leak occurs because the function fails to properly release allocated memory resources after completing blitting operations, creating a gradual accumulation of unused memory that eventually leads to system instability.
The technical implementation of this vulnerability involves the improper handling of memory contexts during graphics command processing. When the vrend_renderer_init_blit_ctx function initializes blitting contexts, it allocates memory structures to handle graphics operations but does not consistently free these allocations when the contexts are no longer needed. This pattern is particularly dangerous in virtualized environments where guest operating systems can directly interact with the graphics subsystem through virglrenderer. The VIRGL_CCMD_BLIT commands are used to perform graphics blitting operations, which are fundamental to rendering graphics in virtualized environments, making this vulnerability particularly impactful as it can be triggered through normal graphics operations.
From an operational impact perspective, this vulnerability enables a local guest user to perform a denial of service attack against the host system by consuming available memory resources. The memory leak gradually consumes host memory until system performance degrades significantly or the system becomes unresponsive due to memory exhaustion. This type of attack is particularly concerning in multi-tenant virtualization environments where one guest user could potentially impact other users or system services running on the same host. The vulnerability's impact extends beyond simple resource exhaustion as it can lead to complete system instability and require manual intervention to restore normal operations, including potential host system reboots.
The vulnerability aligns with CWE-401, which describes improper handling of memory allocation and deallocation, specifically focusing on memory leaks that occur when allocated memory is not properly freed. This weakness is commonly exploited in virtualization environments where guest operating systems have access to graphics subsystems and can leverage these interfaces to perform resource exhaustion attacks. From an ATT&CK framework perspective, this vulnerability maps to the technique T1499.003, which involves resource exhaustion via memory consumption, and potentially T1059, which covers execution through command and scripting interfaces. The attack vector is particularly relevant in cloud computing and virtualization environments where multiple users share the same physical infrastructure, making the potential for cascading failures and service disruption significant.
Mitigation strategies for CVE-2017-5993 primarily involve upgrading to virglrenderer version 0.6.0 or later, where the memory leak has been addressed through proper memory management practices. System administrators should implement monitoring solutions to detect unusual memory consumption patterns that could indicate exploitation attempts. Additionally, virtualization administrators should consider implementing resource limits and quotas for guest operating systems to prevent single users from consuming excessive host resources. The fix implemented in version 0.6.0 likely involved proper memory deallocation mechanisms and context management to ensure that all allocated resources are freed when blitting contexts are destroyed, addressing the root cause of the memory leak through improved code quality and resource management practices.