CVE-2018-6412 in Linux
Summary
by MITRE
In the function sbusfb_ioctl_helper() in drivers/video/fbdev/sbuslib.c in the Linux kernel through 4.15, an integer signedness error allows arbitrary information leakage for the FBIOPUTCMAP_SPARC and FBIOGETCMAP_SPARC commands.
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Analysis
by VulDB Data Team • 02/03/2023
The vulnerability identified as CVE-2018-6412 resides within the Linux kernel's framebuffer subsystem, specifically in the sbusfb_ioctl_helper() function located in drivers/video/fbdev/sbuslib.c. This flaw affects Linux kernel versions through 4.15 and represents a critical security issue that enables unauthorized information disclosure through improper handling of ioctl commands. The vulnerability manifests when processing FBIOPUTCMAP_SPARC and FBIOGETCMAP_SPARC commands, which are used for color map operations on Sparc-based framebuffer devices.
The technical root cause of this vulnerability stems from an integer signedness error that occurs during the validation of color map parameters. When the kernel processes these specific ioctl commands, it fails to properly validate the signedness of integer values used to determine the size and bounds of color map data structures. This improper validation creates a scenario where malicious actors can manipulate the input parameters to bypass size checks and access memory regions that should remain protected. The signedness error allows attackers to cause integer overflow conditions that result in buffer overreads, enabling them to read arbitrary kernel memory locations.
The operational impact of this vulnerability is significant as it provides attackers with the ability to perform arbitrary information leakage from kernel memory spaces. This information disclosure can expose sensitive kernel data structures, memory addresses, and potentially confidential information that could aid in further exploitation attempts. The vulnerability affects systems running on Sparc architecture that utilize framebuffer devices, making it particularly concerning for embedded systems and server environments that rely on these architectures. The disclosed information could include kernel pointers, stack contents, or other sensitive data that could be leveraged for privilege escalation or additional attack vectors.
From a cybersecurity perspective, this vulnerability aligns with CWE-191, which describes integer underflow or overflow conditions, and represents a classic example of how improper input validation can lead to information disclosure. The vulnerability also maps to ATT&CK technique T1005, which covers data from local system, as it allows unauthorized access to kernel memory contents. The attack surface is limited to systems using Sparc-based framebuffer devices, but the potential for information disclosure remains severe. Organizations should prioritize patching affected kernel versions to prevent exploitation, as the vulnerability does not require elevated privileges to trigger the information leakage mechanism. The fix typically involves correcting the integer signedness handling in the ioctl parameter validation logic to ensure proper bounds checking and prevent unauthorized memory access patterns.
This vulnerability demonstrates the importance of rigorous input validation in kernel space operations, particularly when dealing with ioctl commands that manipulate hardware-specific data structures. The integer signedness error represents a subtle but critical flaw that can be exploited to bypass security mechanisms designed to protect kernel memory integrity. Proper kernel development practices should include comprehensive testing of integer operations, especially in functions that handle user-supplied parameters for hardware device interactions.