CVE-2018-16862 in Linux
Summary
by MITRE
A security flaw was found in the Linux kernel in a way that the cleancache subsystem clears an inode after the final file truncation (removal). The new file created with the same inode may contain leftover pages from cleancache and the old file data instead of the new one.
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Analysis
by VulDB Data Team • 06/11/2023
The vulnerability identified as CVE-2018-16862 resides within the Linux kernel's cleancache subsystem, representing a critical data integrity issue that can lead to information disclosure and potential system compromise. This flaw manifests during the file truncation process when the kernel fails to properly clear cached pages associated with an inode, creating a scenario where subsequent file operations may inadvertently expose stale data from previous file contents.
The technical implementation of this vulnerability stems from improper synchronization between the cleancache subsystem and the inode management mechanisms within the Linux kernel. When a file undergoes final truncation, the cleancache subsystem should completely invalidate all cached pages associated with that inode to prevent any possibility of data leakage. However, the flaw allows cached pages to persist even after the file has been truncated, creating a window where new files created with the same inode may contain fragments of the previous file's data. This occurs because the kernel's memory management subsystem does not properly invalidate the cleancache entries during the inode reuse process, leading to a state where old cached pages can be served in response to new file operations.
The operational impact of CVE-2018-16862 extends beyond simple data leakage, potentially enabling attackers to perform cross-file information disclosure attacks. An attacker who can control file creation and truncation patterns may exploit this vulnerability to recover sensitive information from previously deleted files or to gain insights into other processes' data. The vulnerability particularly affects systems that rely heavily on file system caching mechanisms and could be leveraged in scenarios involving temporary file creation, database operations, or any application that frequently truncates and recreates files with the same inode. This flaw aligns with CWE-200, which addresses improper handling of sensitive information, and represents a specific implementation weakness in the Linux kernel's memory management subsystem.
Systems utilizing the cleancache feature, particularly those running older kernel versions or distributions that have not applied the relevant security patches, face significant risk from this vulnerability. The exploitability of CVE-2018-16862 depends on specific conditions including the ability to perform file truncation operations and control the file system's inode reuse patterns. Organizations should prioritize applying kernel security updates that address this cleancache invalidation issue, as the vulnerability can be exploited to recover sensitive data from files that should have been deleted or overwritten. The remediation strategy involves updating to kernel versions that properly implement inode cache invalidation during file truncation operations, with particular attention to the specific kernel version patches that address the cleancache subsystem behavior. This vulnerability demonstrates the importance of proper cache invalidation mechanisms in operating system design and aligns with ATT&CK technique T1005, which covers data from local system, as it enables unauthorized data access through improper cache management.