CVE-2016-8577 in QEMU
Summary
by MITRE
Memory leak in the v9fs_read 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 related to an I/O read operation.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 09/29/2022
The vulnerability identified as CVE-2016-8577 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_read function located in the hw/9pfs/9p.c source file, where improper memory handling during I/O read operations creates conditions for persistent memory consumption that can ultimately exhaust system resources. The vulnerability operates through the 9p filesystem protocol implementation that QEMU uses to provide filesystem access to guest operating systems, making it particularly dangerous in virtualized environments where guest administrators have elevated privileges. When exploited, this memory leak allows local guest OS administrators to repeatedly perform read operations that consume system memory without proper cleanup, leading to gradual resource exhaustion and system instability.
The technical root cause of this vulnerability stems from inadequate memory deallocation practices within the v9fs_read function, which fails to properly release allocated memory blocks after processing read requests. This memory leak occurs during the handling of I/O read operations through the 9p protocol interface, where the function processes guest requests to read filesystem data but does not consistently free previously allocated memory structures. The flaw is classified under CWE-401 as a failure to release memory resources, representing a classic memory management error that can be exploited by malicious actors with access to the guest operating system. The vulnerability specifically manifests when multiple read operations are performed in sequence, with each operation contributing to the accumulation of unreleased memory segments that gradually consume available system resources.
The operational impact of CVE-2016-8577 extends beyond simple resource exhaustion, as it can effectively disable virtualized environments by consuming all available memory on the host system. Local guest administrators who understand the vulnerability can exploit it to create sustained memory consumption patterns that may take hours or days to fully manifest, making detection difficult and potentially allowing for prolonged system degradation. The vulnerability is particularly concerning in multi-tenant cloud environments where multiple guest operating systems share the same host infrastructure, as a single compromised guest could potentially affect the entire host system's stability. Attackers can leverage this weakness to perform persistent resource consumption attacks that may be difficult to distinguish from legitimate system behavior, especially when the memory leak occurs gradually rather than through immediate system crashes.
Mitigation strategies for CVE-2016-8577 should focus on both immediate patching and operational security measures to protect virtualized environments. The most effective immediate solution involves applying the official QEMU patch that corrects the memory deallocation logic in the v9fs_read function, ensuring that all allocated memory blocks are properly freed after each read operation. Organizations should implement strict access controls and privilege management within virtualized environments to limit guest administrator capabilities, reducing the attack surface for potential exploitation. Network segmentation and monitoring systems should be deployed to detect unusual memory consumption patterns that may indicate exploitation attempts, particularly when monitoring virtualized host systems for sustained memory usage increases. Additionally, implementing regular system audits and vulnerability assessments specifically targeting QEMU implementations can help identify and remediate similar memory management issues before they can be exploited. The vulnerability aligns with ATT&CK technique T1499.001 which involves resource exhaustion attacks, making it particularly relevant for organizations implementing cybersecurity frameworks that address denial of service threats in virtualized environments.