CVE-2016-9102 in QEMU
Summary
by MITRE
Memory leak in the v9fs_xattrcreate function in hw/9pfs/9p.c in QEMU (aka Quick Emulator) allows local guest OS administrators to cause a denial of service (memory consumption and QEMU process crash) via a large number of Txattrcreate messages with the same fid number.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability CVE-2016-9102 represents a critical memory leak issue within the QEMU virtualization platform that specifically affects the v9fs_xattrcreate function in the 9p.c file. This flaw exists in the handling of 9p filesystem protocol messages within the QEMU hypervisor environment, where the virtual machine's guest operating system can exploit this weakness to consume excessive system resources. The vulnerability is particularly concerning because it allows local guest administrators to manipulate the memory allocation patterns of the QEMU process through carefully crafted sequences of Txattrcreate messages, effectively creating a denial of service condition that can lead to system instability and potential crashes.
The technical implementation of this vulnerability stems from insufficient memory management within the 9p filesystem implementation in QEMU's 9p.c file. When processing Txattrcreate messages, the v9fs_xattrcreate function fails to properly release allocated memory resources when handling multiple requests with identical fid numbers. This memory leak occurs because the function does not adequately track or clean up memory allocations that are associated with repeated operations on the same file identifier, creating a gradual accumulation of unused memory that eventually exhausts available system resources. The flaw is classified as a CWE-401 Memory Leak, which is a fundamental weakness in resource management that can lead to resource exhaustion and system instability.
The operational impact of this vulnerability extends beyond simple resource consumption, as it can be leveraged to cause complete system crashes in the QEMU virtualization environment. Local guest administrators with access to the virtual machine can repeatedly send Txattrcreate messages with identical fid numbers, causing the QEMU process to continuously allocate memory without proper cleanup. This results in progressive memory consumption that can eventually lead to the QEMU process being terminated by the operating system's memory management subsystem or causing the entire virtual machine to become unresponsive. The vulnerability affects all versions of QEMU that implement the 9p filesystem protocol, making it a widespread concern for virtualization environments that utilize this functionality.
From a cybersecurity perspective, this vulnerability aligns with ATT&CK technique T1499.001 which involves resource exhaustion attacks, and represents a classic example of how virtualization platforms can be exploited to compromise system availability. The attack vector requires local access within the guest operating system, making it a privilege escalation issue that can be particularly dangerous in multi-tenant virtualization environments where guest administrators might have limited access but can still cause significant disruption. The vulnerability also demonstrates the importance of proper memory management in hypervisor components, as failures in resource cleanup within virtualization layers can have cascading effects on system stability. Organizations using QEMU for virtualization should implement immediate mitigations including applying the relevant security patches, monitoring memory usage patterns in virtualized environments, and implementing network segmentation to limit guest access to potentially vulnerable filesystem protocols.
This vulnerability highlights the critical need for comprehensive memory management practices in virtualization software, particularly in components that handle network protocols and filesystem operations. The flaw serves as a reminder that even seemingly benign operations within hypervisor components can be exploited to cause significant system instability, and proper input validation and resource cleanup mechanisms are essential for maintaining system integrity. The memory leak pattern described in CVE-2016-9102 demonstrates how repeated operations with identical parameters can create conditions for resource exhaustion attacks, emphasizing the importance of robust memory management practices in virtualization environments. Organizations should prioritize updating their QEMU installations to versions that address this vulnerability while also implementing monitoring solutions that can detect unusual memory consumption patterns that might indicate exploitation attempts.