CVE-2015-8374 in Linux
Summary
by MITRE
fs/btrfs/inode.c in the Linux kernel before 4.3.3 mishandles compressed inline extents, which allows local users to obtain sensitive pre-truncation information from a file via a clone action.
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Analysis
by VulDB Data Team • 07/01/2022
The vulnerability identified as CVE-2015-8374 resides within the Linux kernel's Btrfs filesystem implementation, specifically in the fs/btrfs/inode.c file. This flaw represents a critical information disclosure issue that affects kernel versions prior to 4.3.3, creating a significant security risk for systems utilizing the Btrfs filesystem. The vulnerability stems from improper handling of compressed inline extents during file clone operations, which exposes pre-truncation data that should remain inaccessible to local users.
The technical root cause of this vulnerability lies in the kernel's insufficient validation and management of compressed inline extents when performing clone actions on Btrfs filesystem files. When a file is cloned, the system should properly handle the compression state and ensure that no sensitive data from the original file's pre-truncation state leaks into the cloned copy. However, the flawed implementation fails to adequately sanitize these compressed extents, allowing attackers to access data that was previously truncated or overwritten but still exists in the underlying storage structure.
This vulnerability operates under the attack pattern classified as CWE-200 Information Exposure, where the system inadvertently reveals sensitive information to unauthorized users. The operational impact is particularly concerning for local users who can exploit this flaw without requiring remote access privileges. The attack vector involves a local user executing a clone operation on a file containing compressed inline extents, which triggers the information leak. The vulnerability does not require elevated privileges for exploitation, making it particularly dangerous in multi-user environments where local access is common.
The security implications extend beyond simple information disclosure, as the leaked pre-truncation data could contain sensitive content such as passwords, cryptographic keys, personal information, or other confidential data that was previously thought to be securely removed from the filesystem. This represents a violation of data confidentiality principles and could potentially lead to further exploitation if the leaked information contains credentials or other attack vectors. The vulnerability affects systems where Btrfs is the primary filesystem and where local users might have the ability to perform file clone operations.
Mitigation strategies for this vulnerability require immediate kernel updates to version 4.3.3 or later, which contain the necessary patches to properly handle compressed inline extents during clone operations. System administrators should prioritize patching affected systems and verify that the kernel version is properly updated across all Btrfs filesystem installations. Additional monitoring should be implemented to detect unusual clone operations on sensitive files, and access controls should be reviewed to limit local user capabilities where possible. The fix addresses the core issue by ensuring proper validation of compressed extent states during file operations, preventing the leakage of pre-truncation data through the clone mechanism. Organizations should also consider implementing filesystem-level monitoring to detect potential exploitation attempts and maintain comprehensive audit logs of file operations on Btrfs volumes.