CVE-2007-6417 in Linux
Summary
by MITRE
The shmem_getpage function (mm/shmem.c) in Linux kernel 2.6.11 through 2.6.23 does not properly clear allocated memory in some rare circumstances related to tmpfs, which might allow local users to read sensitive kernel data or cause a denial of service (crash).
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Analysis
by VulDB Data Team • 07/30/2021
The vulnerability described in CVE-2007-6417 resides within the Linux kernel's shared memory implementation, specifically in the shmem_getpage function located in mm/shmem.c. This flaw affects kernel versions ranging from 2.6.11 through 2.6.23, representing a significant portion of the linux 2.6.x kernel series that was widely deployed in enterprise and server environments during that timeframe. The vulnerability operates at the kernel level and specifically targets the tmpfs filesystem implementation which provides temporary file storage in memory. The issue manifests when the kernel allocates memory pages for tmpfs files but fails to properly clear the allocated memory before returning it to user space applications, creating a potential information disclosure risk.
The technical nature of this vulnerability stems from improper memory clearing operations within the shared memory subsystem. When the shmem_getpage function handles memory allocation for tmpfs files, it occasionally leaves residual data from previous kernel operations in the allocated memory pages. This occurs during rare circumstances that involve specific patterns of memory allocation and deallocation within the tmpfs implementation. The function fails to ensure complete memory sanitization before returning pages to applications, potentially leaving kernel memory contents accessible to local users who can read the allocated pages through normal file operations. This memory leakage can expose sensitive kernel data including cryptographic keys, passwords, or other confidential information that was previously stored in the cleared memory areas.
The operational impact of this vulnerability presents multiple security concerns for affected systems. Local users with access to tmpfs filesystems can exploit this weakness to read kernel memory contents, potentially exposing sensitive data that should remain protected within kernel space. The information disclosure aspect of this vulnerability aligns with CWE-200, which covers improper output handling vulnerabilities that can lead to information exposure. Additionally, the vulnerability can be leveraged to cause denial of service conditions when the improper memory handling triggers kernel crashes or system instability. Attackers could potentially use this weakness to repeatedly trigger memory allocation patterns that cause system crashes, effectively creating a persistent denial of service scenario. The vulnerability also maps to ATT&CK technique T1068, which involves exploiting local privilege escalation opportunities to gain unauthorized access to system resources.
Mitigation strategies for CVE-2007-6417 focus on kernel updates and system hardening measures. The most effective approach involves upgrading to a patched kernel version that addresses the memory clearing issue in the shmem_getpage function. Organizations should prioritize patch management to ensure all systems running affected kernel versions receive the necessary security updates. System administrators can also implement additional monitoring to detect unusual memory access patterns that might indicate exploitation attempts. The vulnerability highlights the importance of proper memory management practices in kernel code, particularly when dealing with shared memory implementations that handle sensitive data. Security teams should consider implementing least privilege access controls for tmpfs filesystems and monitor for unauthorized access to temporary file storage areas. This vulnerability demonstrates the critical nature of kernel-level memory sanitization and the potential consequences of inadequate memory clearing operations in operating system components.