CVE-2011-4086 in Linux
Summary
by MITRE
The journal_unmap_buffer function in fs/jbd2/transaction.c in the Linux kernel before 3.3.1 does not properly handle the _Delay and _Unwritten buffer head states, which allows local users to cause a denial of service (system crash) by leveraging the presence of an ext4 filesystem that was mounted with a journal.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 03/20/2021
The vulnerability identified as CVE-2011-4086 represents a critical flaw in the Linux kernel's journaling subsystem that affects systems running kernel versions prior to 3.3.1. This issue specifically targets the journal_unmap_buffer function located within the fs/jbd2/transaction.c file, which is responsible for managing the buffer head states during ext4 filesystem operations. The flaw arises from inadequate handling of two specific buffer head states: _Delay and _Unwritten, creating a condition where malicious local users can exploit this weakness to trigger system crashes and denial of service conditions.
The technical root cause of this vulnerability stems from the improper state management within the journaling mechanism that governs how ext4 filesystems handle data consistency and recovery operations. When an ext4 filesystem is mounted with a journal, the kernel must maintain proper tracking of buffer head states to ensure data integrity during transactions. The journal_unmap_buffer function fails to correctly process buffer heads that are in _Delay or _Unwritten states, which can occur during normal filesystem operations but become exploitable when manipulated by a local user. This improper handling creates a path where buffer head inconsistencies can lead to kernel memory corruption and ultimately system crashes.
The operational impact of CVE-2011-4086 extends beyond simple denial of service, as it represents a fundamental weakness in the kernel's transaction management system that can be leveraged by local attackers with minimal privileges. Since the vulnerability requires only local access to exploit, it poses a significant risk in multi-user environments where untrusted users might have shell access to systems running vulnerable kernel versions. The attack vector is particularly concerning because it can be executed through normal filesystem operations, making it difficult to detect and prevent through standard security monitoring approaches. Systems running affected kernel versions are susceptible to spontaneous reboots and system instability that can result in data loss and service interruptions.
This vulnerability aligns with CWE-121, which describes improper handling of buffer head states in kernel memory management, and represents a classic example of a memory safety issue that can be exploited through local privilege escalation or denial of service attacks. The ATT&CK framework categorizes this as a system service denial of service technique where adversaries leverage kernel-level flaws to disrupt system availability. Organizations should prioritize patching systems running kernel versions before 3.3.1 to address this vulnerability, as the fix involves proper state management in the journaling subsystem. The mitigation strategy should include comprehensive kernel updates across all affected systems, particularly those running ext4 filesystems with journaling enabled, and monitoring for potential exploitation attempts through unusual system crash patterns or filesystem error messages that might indicate buffer head state corruption.
The vulnerability demonstrates how seemingly minor inconsistencies in kernel transaction management can result in catastrophic system failures, highlighting the importance of rigorous testing and validation of filesystem journaling mechanisms. This flaw underscores the critical nature of maintaining up-to-date kernel versions and implementing proper security controls to prevent local users from exploiting kernel-level vulnerabilities that can compromise system availability and stability.