CVE-2016-9685 in Linux
Summary
by MITRE
Multiple memory leaks in error paths in fs/xfs/xfs_attr_list.c in the Linux kernel before 4.5.1 allow local users to cause a denial of service (memory consumption) via crafted XFS filesystem operations.
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Analysis
by VulDB Data Team • 10/12/2022
The vulnerability identified as CVE-2016-9685 represents a critical memory management flaw within the Linux kernel's XFS filesystem implementation. This issue specifically affects the xfs_attr_list.c file where multiple memory leaks occur during error handling paths, creating a persistent resource exhaustion condition that can be exploited by local attackers. The vulnerability exists in Linux kernel versions prior to 4.5.1, making a substantial portion of deployed systems susceptible to this attack vector. The flaw manifests when crafted XFS filesystem operations are performed, triggering error conditions that fail to properly release allocated memory resources, resulting in gradual memory consumption over time.
The technical nature of this vulnerability stems from improper memory deallocation within the XFS attribute listing functionality when error conditions are encountered. During normal operation, the XFS filesystem maintains various data structures to track attribute information associated with files and directories. When operations fail or encounter exceptional conditions, the kernel's error handling routines should ensure that all allocated memory is properly freed. However, in this case, specific error paths in the xfs_attr_list.c file do not execute proper cleanup operations, leading to memory leaks that accumulate over time. This type of vulnerability falls under the CWE-401 weakness category, which specifically addresses improper management of memory allocation and deallocation, making it a classic example of resource leak exploitation.
The operational impact of CVE-2016-9685 extends beyond simple resource exhaustion, creating a potential denial of service condition that can severely impact system stability and performance. Local users with access to the affected system can repeatedly perform crafted XFS operations to gradually consume available memory, eventually leading to system slowdowns, application failures, or complete system unresponsiveness. The vulnerability is particularly dangerous because it operates silently in the background, with memory consumption occurring incrementally rather than causing immediate system crashes. This characteristic makes it difficult to detect and can lead to extended periods of degraded system performance before the full impact becomes apparent, potentially affecting critical system services and user applications that depend on adequate memory resources.
Mitigation strategies for CVE-2016-9685 primarily focus on upgrading to Linux kernel versions 4.5.1 or later where the memory leak has been addressed through proper error handling implementation. System administrators should prioritize patching affected systems, particularly those running older kernel versions where the vulnerability exists. Additionally, monitoring system memory usage patterns can help detect potential exploitation attempts, though this approach provides only reactive detection rather than prevention. The vulnerability demonstrates the importance of thorough error handling in kernel space code, where improper resource management can have cascading effects on system stability. Organizations should implement regular kernel update schedules and maintain awareness of security advisories from kernel maintainers and security vendors. This vulnerability also highlights the need for comprehensive testing of error paths in kernel modules, as the issue was present in production systems for an extended period before detection and remediation. The ATT&CK framework categorizes this vulnerability under privilege escalation and denial of service techniques, where local users can leverage memory leaks to exhaust system resources and compromise service availability.