CVE-2015-8961 in Android
Summary
by MITRE • 01/25/2023
The __ext4_journal_stop function in fs/ext4/ext4_jbd2.c in the Linux kernel before 4.3.3 allows local users to gain privileges or cause a denial of service (use-after-free) by leveraging improper access to a certain error field.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 01/25/2023
The vulnerability identified as CVE-2015-8961 resides within the ext4 filesystem implementation of the Linux kernel, specifically in the __ext4_journal_stop function located in fs/ext4/ext4_jbd2.c. This flaw represents a critical security weakness that affects Linux kernel versions prior to 4.3.3, creating potential pathways for privilege escalation and system instability. The vulnerability manifests through improper handling of error fields during journal operations, which are fundamental to maintaining filesystem consistency and data integrity in ext4 implementations.
The technical root cause of this vulnerability stems from a use-after-free condition that occurs when the __ext4_journal_stop function processes error states during journal commit operations. When an error occurs during filesystem journaling, the function fails to properly manage memory references to error structures, leading to situations where freed memory locations may still be accessed or modified by subsequent operations. This improper memory management creates opportunities for attackers to manipulate the error field in ways that can trigger arbitrary code execution or system crashes. The vulnerability specifically impacts the journal stop mechanism that is crucial for ensuring data consistency when transactions are committed to the ext4 filesystem.
From an operational perspective, this vulnerability presents significant risks to Linux systems running affected kernel versions. Local attackers with minimal privileges can exploit this weakness to either escalate their privileges to root level access or to cause denial of service conditions that effectively crash the system. The use-after-free condition can be leveraged to execute arbitrary code within kernel space, potentially allowing attackers to bypass security controls and gain complete system control. The impact extends beyond simple privilege escalation as the vulnerability can also be used to create persistent backdoors or to corrupt filesystem data, leading to data loss and system instability that may require complete system reinstallation.
Mitigation strategies for CVE-2015-8961 primarily focus on kernel version upgrades to 4.3.3 or later, which contain the necessary patches to address the improper error field access. System administrators should prioritize applying these updates across all affected systems, particularly those running ext4 filesystems with high security requirements. Additional protective measures include implementing kernel lockdown mechanisms, disabling unnecessary filesystem features, and monitoring for unusual system behavior that might indicate exploitation attempts. The vulnerability aligns with CWE-416, which describes use-after-free errors, and can be categorized under ATT&CK technique T1068, involving exploit for privilege escalation, making it a significant concern for enterprise security teams managing Linux infrastructure. Organizations should also consider implementing intrusion detection systems that can identify potential exploitation attempts and maintain comprehensive backup and recovery procedures to address potential system compromise scenarios.