CVE-2016-7155 in QEMU
Summary
by MITRE
hw/scsi/vmw_pvscsi.c in QEMU (aka Quick Emulator) allows local guest OS administrators to cause a denial of service (out-of-bounds access or infinite loop, and QEMU process crash) via a crafted page count for descriptor rings.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-7155 resides within the VMware Paravirtualized SCSI (pvscsi) device implementation in QEMU, specifically in the hw/scsi/vmw_pvscsi.c file. This issue affects virtualized environments where guest operating systems utilize the pvscsi controller for SCSI device emulation. The flaw manifests when a local guest OS administrator manipulates the page count parameter associated with descriptor rings, creating conditions that can lead to system instability and service disruption.
The technical root cause involves insufficient input validation and boundary checking within the pvscsi device driver implementation. When a guest OS administrator crafts a malicious page count value for descriptor rings, the QEMU emulator fails to properly validate this input before processing. This validation gap enables attackers to trigger out-of-bounds memory access patterns or induce infinite loop conditions within the QEMU process execution environment. The vulnerability specifically targets the descriptor ring management logic that handles SCSI command processing between the guest and hypervisor layers.
From an operational impact perspective, this vulnerability represents a significant security risk for virtualized infrastructures as it allows local privilege escalation within guest environments to achieve denial of service against the host hypervisor. The QEMU process crash resulting from this vulnerability can lead to complete system unavailability, disrupting critical services and potentially affecting multiple virtual machines running on the same host. Attackers exploiting this flaw can effectively render virtualized environments unusable, causing business disruption and potential data loss.
The vulnerability aligns with CWE-129, which addresses insufficient validation of length fields, and demonstrates characteristics consistent with CWE-674, involving uncontrolled resource consumption through infinite loops. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, specifically targeting virtualization and container environments through resource exhaustion and service disruption techniques. The attack vector requires local access within the guest OS but leverages the hypervisor's trust relationship with virtualized devices to escalate impact beyond the guest boundary.
Mitigation strategies should include immediate patching of QEMU versions containing the vulnerable pvscsi implementation, implementing strict input validation policies for virtual device parameters, and deploying monitoring solutions to detect anomalous page count values in descriptor rings. Network segmentation and virtual machine isolation can help limit the potential impact, while regular security audits of virtualization components should verify proper implementation of boundary checking mechanisms. Organizations should also consider implementing automated patch management systems to ensure timely remediation of similar vulnerabilities in virtualization infrastructure components.