CVE-2017-8086 in QEMU
Summary
by MITRE
Memory leak in the v9fs_list_xattr function in hw/9pfs/9p-xattr.c in QEMU (aka Quick Emulator) allow local guest OS privileged users to cause a denial of service (memory consumption) via vectors involving the orig_value variable.
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Analysis
by VulDB Data Team • 12/02/2022
The vulnerability identified as CVE-2017-8086 represents a critical memory management flaw within the QEMU virtualization platform that specifically affects the v9fs_list_xattr function implementation. This issue resides in the hw/9pfs/9p-xattr.c file and demonstrates a classic memory leak pattern that can be exploited by local privileged users within the guest operating system. The vulnerability occurs when processing extended attributes in the 9p filesystem implementation, where the orig_value variable fails to be properly deallocated, leading to progressive memory consumption that can ultimately result in system instability or complete denial of service conditions.
The technical root cause of this vulnerability stems from improper memory management within the virtual filesystem layer that QEMU employs to facilitate communication between guest and host systems. When the v9fs_list_xattr function processes extended attribute requests, it allocates memory for the orig_value variable but fails to release this memory allocation upon function completion. This memory leak occurs in the context of 9p protocol implementation which is used for file system sharing between virtual machines and their host environments. The flaw specifically manifests when handling extended attributes, which are metadata entries that provide additional information about files and directories beyond standard file system attributes. This type of vulnerability is categorized under CWE-401 as "Improper Release of Memory Before Removing Last Reference" and demonstrates the classic symptoms of memory resource exhaustion that can be exploited through repeated invocation of the vulnerable code path.
The operational impact of CVE-2017-8086 extends beyond simple resource consumption to potentially compromise the stability and availability of virtualized environments. Local privileged users within the guest operating system can repeatedly invoke the vulnerable function to gradually consume available memory on the host system, eventually leading to system performance degradation or complete system crashes. This vulnerability is particularly dangerous in multi-tenant virtualization environments where one compromised guest could potentially impact other virtual machines running on the same host. The attack vector requires local access and privileged execution within the guest OS, making it less immediately exploitable than remote attacks but still highly concerning for security-conscious deployments. From an attack perspective, this vulnerability aligns with ATT&CK technique T1499.001 "Fork Bomb" and T1070.004 "File Deletion" as it demonstrates resource exhaustion capabilities that can be leveraged for denial of service attacks within virtualized environments.
Mitigation strategies for this vulnerability should focus on both immediate patching and operational security measures. The primary solution involves applying the official QEMU patch that properly deallocates the orig_value variable in the v9fs_list_xattr function, ensuring that all memory allocations are correctly released upon function completion. Organizations should prioritize updating their QEMU installations to versions that contain the fix, typically QEMU 2.10.0 or later, which addresses this specific memory leak issue. Additionally, implementing monitoring solutions to detect unusual memory consumption patterns within virtualized environments can help identify potential exploitation attempts. System administrators should also consider implementing resource limits and quotas for virtual machines to prevent a single guest from consuming excessive host resources. Network segmentation and access controls can further reduce the attack surface by limiting local privileged access within guest systems, thereby reducing the likelihood of exploitation. The vulnerability serves as a reminder of the importance of proper memory management in virtualization platforms and highlights the need for comprehensive security testing of virtualization components that handle user input and system resources.