CVE-2011-1833 in Linux
Summary
by MITRE
Race condition in the ecryptfs_mount function in fs/ecryptfs/main.c in the eCryptfs subsystem in the Linux kernel before 3.1 allows local users to bypass intended file permissions via a mount.ecryptfs_private mount with a mismatched uid.
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Analysis
by VulDB Data Team • 12/14/2021
The vulnerability described in CVE-2011-1833 represents a critical race condition within the eCryptfs subsystem of the Linux kernel, specifically affecting versions prior to 3.1. This flaw exists in the ecryptfs_mount function located in fs/ecryptfs/main.c and fundamentally undermines the security model designed to protect encrypted file systems. The eCryptfs subsystem provides transparent file system encryption for Linux systems, allowing users to encrypt individual files or entire directories while maintaining seamless access to the encrypted data. The vulnerability arises from improper handling of mount operations when using the mount.ecryptfs_private mount option, creating a window where malicious users can exploit timing discrepancies in the permission checking process.
The technical implementation of this race condition occurs when a local user attempts to mount an eCryptfs file system with the mount.ecryptfs_private option while simultaneously manipulating the uid parameter. During the mount operation, the kernel fails to properly synchronize access to critical data structures that determine file permissions, allowing an attacker to exploit the timing gap between when permission checks are initially performed and when final authorization decisions are made. This race condition specifically manifests when the mount operation involves a mismatched uid, where the user attempting the mount operation does not match the expected ownership of the encrypted file system. The flaw enables unauthorized access to files that should be restricted to specific users, effectively bypassing the intended access controls that eCryptfs is designed to enforce.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it fundamentally compromises the confidentiality and integrity of encrypted data stored on affected systems. Local users who can exploit this race condition gain unauthorized access to encrypted files that were intended to be protected from their own access or from access by other users. This represents a significant breach in the security model, as the vulnerability allows users to circumvent the very protections that encryption is meant to provide. The attack vector requires local system access and knowledge of the specific mount options, but once exploited, it can result in complete data exposure and potential further privilege escalation within the system. The vulnerability affects systems running Linux kernel versions 2.6.37 and earlier, making it particularly concerning for legacy systems that may not have received timely security updates.
Mitigation strategies for this vulnerability focus on both immediate system updates and operational security improvements. The primary and most effective solution involves upgrading to Linux kernel version 3.1 or later, where the race condition has been properly addressed through improved synchronization mechanisms and enhanced permission checking procedures. System administrators should prioritize patching affected systems and ensure that all kernel components are updated to versions that contain the relevant security fixes. Additionally, organizations should implement strict monitoring of mount operations and access patterns to detect potential exploitation attempts. The vulnerability aligns with CWE-362, which describes race conditions in security-critical code sections, and can be mapped to ATT&CK technique T1068, which covers local privilege escalation through kernel vulnerabilities. Security teams should also consider implementing least privilege principles for mount operations and regularly auditing encrypted file system access controls to prevent unauthorized data exposure.