CVE-2016-9105 in QEMU
Summary
by MITRE
Memory leak in the v9fs_link function in hw/9pfs/9p.c in QEMU (aka Quick Emulator) allows local guest OS administrators to cause a denial of service (memory consumption) via vectors involving a reference to the source fid object.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-9105 represents a critical memory management flaw within QEMU's 9p filesystem implementation that exposes systems to potential denial of service attacks. This issue specifically affects the v9fs_link function located in the hw/9pfs/9p.c file, where improper handling of file identifier objects creates persistent memory allocation issues. The vulnerability arises from the failure to properly release reference counts on source fid objects during link operations, creating a condition where memory resources accumulate over time without being freed. Attackers exploiting this weakness can leverage the local guest operating system administrator privileges to repeatedly invoke link operations that generate memory leaks, ultimately consuming available system memory and causing system instability or complete denial of service.
The technical nature of this vulnerability aligns with CWE-401, which catalogs weakness categories related to improper handling of memory allocation and deallocation. The flaw demonstrates characteristics of resource leak vulnerabilities where allocated memory structures remain unreleased, creating a gradual degradation of system performance. Within the context of QEMU's virtualization environment, this vulnerability operates at the hypervisor level where guest operating systems maintain administrative privileges that can be abused to manipulate the virtualized filesystem services. The attack vector specifically targets the 9p protocol implementation that QEMU uses to provide filesystem sharing between host and guest systems, making it particularly dangerous in virtualized environments where multiple guests may be running simultaneously.
The operational impact of CVE-2016-9105 extends beyond simple resource exhaustion, as it can compromise the stability of entire virtualized infrastructures. When exploited, the memory leak progressively consumes available RAM on the host system, potentially causing other virtual machines to experience resource contention or complete system crashes. This vulnerability is particularly concerning in cloud computing environments where multiple virtual machines share the same physical host, as a single compromised guest could affect the performance and availability of all hosted services. The local privilege requirement means that attackers need administrative access within the guest operating system, but this access is often readily available in many enterprise environments where guest systems are configured with elevated privileges for administrative tasks.
Mitigation strategies for this vulnerability should focus on both immediate patching and operational security improvements. The primary solution involves applying the official QEMU patch that corrects the reference counting logic in the v9fs_link function, ensuring that source fid objects are properly dereferenced after link operations complete. Organizations should implement monitoring systems to detect unusual memory consumption patterns in virtualized environments, particularly when multiple link operations are performed within guest systems. Network segmentation and privilege reduction practices can limit the potential impact of such vulnerabilities by minimizing the administrative access available within guest operating systems. Additionally, implementing automated patch management systems ensures that QEMU versions are kept up to date with security fixes, preventing exploitation of known vulnerabilities. The ATT&CK framework categorizes this vulnerability under privilege escalation and resource exhaustion techniques, emphasizing the need for comprehensive security monitoring and access control measures to prevent exploitation.