CVE-2016-6136 in Android
Summary
by MITRE
Race condition in the audit_log_single_execve_arg function in kernel/auditsc.c in the Linux kernel through 4.7 allows local users to bypass intended character-set restrictions or disrupt system-call auditing by changing a certain string, aka a "double fetch" vulnerability.
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Analysis
by VulDB Data Team • 09/30/2022
The CVE-2016-6136 vulnerability represents a critical race condition flaw within the Linux kernel's auditing subsystem that fundamentally undermines the integrity of system-call logging mechanisms. This vulnerability exists in the audit_log_single_execve_arg function located in kernel/auditsc.c and affects Linux kernel versions through 4.7, creating a dangerous scenario where local attackers can manipulate audit logging behavior through carefully crafted string modifications. The vulnerability stems from a classic double fetch attack pattern where the kernel retrieves a string value twice during the auditing process, allowing an attacker to modify the string content between these two fetch operations, thereby bypassing intended security controls.
The technical implementation of this race condition occurs during the execution of execve system calls where the kernel attempts to log argument strings for auditing purposes. When the audit subsystem processes execve arguments, it first fetches a string value to determine its length and then fetches the same string again to log its contents. This two-step process creates a window where a malicious process can alter the string content between these operations, effectively allowing attackers to modify what gets logged without detection. The vulnerability specifically targets character-set restrictions that are supposed to prevent certain characters from being included in audit logs, enabling attackers to bypass these controls by exploiting the timing gap between string fetches.
From an operational impact perspective, this vulnerability creates significant security implications for system administrators and security professionals who rely on accurate audit logging for compliance, forensic analysis, and threat detection. The ability to bypass character-set restrictions means that malicious actors can potentially hide their activities by manipulating audit log entries to exclude suspicious characters or sequences that would normally trigger security alerts. Additionally, the disruption of system-call auditing can mask unauthorized activities, making it difficult for security teams to maintain accurate logs of system operations and potentially allowing persistent threats to remain undetected for extended periods. This vulnerability directly impacts the integrity and reliability of audit trails that are essential for security monitoring and incident response activities.
The vulnerability aligns with CWE-367, which addresses the dangerous use of a function that can be exploited to bypass security controls, and demonstrates characteristics consistent with ATT&CK technique T1070.006 for Indicator Removal on Host. Organizations implementing Linux-based systems with audit capabilities must recognize that this vulnerability can be exploited to create false audit trails, undermining the effectiveness of security monitoring systems. The race condition nature of this flaw also relates to broader security principles around atomic operations and the need for proper synchronization mechanisms in kernel code. Remediation efforts should focus on patching affected kernel versions, implementing proper synchronization primitives, and ensuring that audit logging mechanisms are designed to prevent such timing-based attacks. System administrators should also consider implementing additional monitoring for unusual audit log patterns that might indicate exploitation attempts, as the vulnerability's impact on audit integrity can be subtle and difficult to detect through conventional means.