CVE-2015-1339 in Linux
Summary
by MITRE
Memory leak in the cuse_channel_release function in fs/fuse/cuse.c in the Linux kernel before 4.4 allows local users to cause a denial of service (memory consumption) or possibly have unspecified other impact by opening /dev/cuse many times.
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Analysis
by VulDB Data Team • 07/09/2022
The vulnerability identified as CVE-2015-1339 represents a critical memory management flaw within the Linux kernel's FUSE (Filesystem in Userspace) subsystem, specifically affecting the cuse_channel_release function located in fs/fuse/cuse.c. This memory leak occurs when the cuse device is repeatedly opened and closed without proper cleanup of allocated memory resources, creating a condition where kernel memory becomes progressively consumed and unreleased. The vulnerability affects Linux kernel versions prior to 4.4, making it a long-standing issue that impacted a significant portion of kernel deployments. The flaw manifests when local users repeatedly open /dev/cuse device nodes, causing the kernel to allocate memory for each channel but failing to properly release it during the cleanup process. This behavior directly violates the principle of proper resource management and can lead to progressive memory exhaustion, ultimately resulting in system instability or complete denial of service conditions. The vulnerability is classified under CWE-401 as a failure to release memory resources, representing a fundamental memory management error that undermines system stability.
The technical exploitation of this vulnerability involves a simple yet effective local attack pattern where an attacker opens the /dev/cuse device multiple times in a loop without properly closing the file descriptors. Each opening operation triggers allocation of kernel memory structures within the cuse_channel_release function, but due to the memory leak, these allocations are never properly freed. The memory consumption grows linearly with each additional open operation, and since the kernel cannot reclaim this memory without proper cleanup, the system's available memory pool gradually diminishes. This type of attack falls under the ATT&CK technique T1499.004 for Network Denial of Service, though it operates at the kernel level rather than network level. The memory leak specifically affects kernel heap management and can be triggered by any local user with access to the /dev/cuse device, making it particularly dangerous in multi-user environments where privilege escalation or resource exhaustion attacks could be employed. The impact extends beyond simple memory consumption, as the continuous depletion of kernel memory can cause system-wide performance degradation, application crashes, and potentially system lockups or reboots when memory pressure becomes severe.
The operational impact of CVE-2015-1339 is significant for system administrators and security professionals managing Linux-based systems, particularly those utilizing FUSE-based filesystems or applications that depend on the cuse subsystem. The vulnerability can be exploited to consume system resources without requiring elevated privileges, making it a low-effort, high-impact attack vector for denial of service scenarios. Systems running kernel versions prior to 4.4 are particularly vulnerable, and the memory leak can be sustained over time, gradually depleting system resources until the system becomes unresponsive. The vulnerability affects not only standalone systems but also virtualized environments and containerized applications that rely on FUSE functionality. Organizations using applications that interface with /dev/cuse, such as FUSE-based filesystems, virtualization tools, or custom kernel modules, face increased risk of service disruption. The attack can be easily automated and sustained, making it particularly dangerous in environments where system uptime is critical. Recovery from such an attack typically requires system reboot to reclaim the leaked memory, as the kernel cannot automatically reclaim the memory without proper cleanup operations. Additionally, the vulnerability demonstrates poor memory management practices within the kernel's FUSE subsystem, highlighting the need for rigorous code review and testing of kernel memory allocation and deallocation functions. This vulnerability underscores the importance of proper resource management in kernel space and the potential for seemingly minor memory leaks to cause significant system instability and availability issues. The fix implemented in kernel version 4.4 addressed the specific memory leak in cuse_channel_release by ensuring proper cleanup of allocated resources during device closure operations, thereby preventing the progressive memory consumption that led to denial of service conditions.