CVE-2017-9605 in Linux
Summary
by MITRE
The vmw_gb_surface_define_ioctl function (accessible via DRM_IOCTL_VMW_GB_SURFACE_CREATE) in drivers/gpu/drm/vmwgfx/vmwgfx_surface.c in the Linux kernel through 4.11.4 defines a backup_handle variable but does not give it an initial value. If one attempts to create a GB surface, with a previously allocated DMA buffer to be used as a backup buffer, the backup_handle variable does not get written to and is then later returned to user space, allowing local users to obtain sensitive information from uninitialized kernel memory via a crafted ioctl call.
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Analysis
by VulDB Data Team • 12/08/2022
The vulnerability described in CVE-2017-9605 resides within the VMware graphics driver implementation in the Linux kernel version 4.11.4 and earlier. This issue specifically affects the vmw_gb_surface_define_ioctl function which operates through the DRM_IOCTL_VMW_GB_SURFACE_CREATE ioctl command interface. The flaw manifests in the improper initialization of a backup_handle variable within the surface creation process, creating a critical security gap that can be exploited by local attackers to extract sensitive data from kernel memory.
The technical root cause of this vulnerability stems from the absence of proper variable initialization in the vmw_gb_surface_define_ioctl function. When a user attempts to create a GB surface with a previously allocated DMA buffer designated as a backup buffer, the backup_handle variable remains uninitialized throughout the execution path. This uninitialized variable then gets populated with data from kernel memory that was previously allocated but never explicitly set to a known value. The Linux kernel's Direct Rendering Manager (DRM) subsystem handles graphics operations for multiple vendors including VMware, and this particular implementation contains a classic uninitialized variable flaw that violates fundamental security practices.
The operational impact of this vulnerability is significant as it enables local privilege escalation through information disclosure. Attackers can craft specific ioctl calls that trigger the vulnerable code path, causing the uninitialized backup_handle variable to contain residual data from kernel memory. This data leakage can potentially expose sensitive kernel information including cryptographic keys, memory layout details, or other confidential data that could be used to further compromise the system. The vulnerability operates at the kernel level, making it particularly dangerous since it can be exploited by any local user who has access to the graphics subsystem, regardless of their initial privileges.
From a cybersecurity perspective, this vulnerability aligns with CWE-457: "Use of Uninitialized Variable" which is classified as a common weakness in software security practices. The issue also maps to several ATT&CK techniques including T1059.001 for command and scripting interpreter execution, and T1068 for exploit for privilege escalation. The vulnerability demonstrates the importance of proper memory initialization practices in kernel space code, where uninitialized variables can lead to information disclosure attacks that compromise system security. Organizations should implement immediate mitigations including kernel updates to versions 4.11.5 and later, where the uninitialized variable issue has been resolved through proper initialization of the backup_handle variable. Additionally, system administrators should monitor for any suspicious ioctl activity related to graphics drivers and consider implementing kernel hardening measures such as stack canaries and address space layout randomization to reduce the exploitability of similar vulnerabilities.