CVE-2016-4964 in QEMU
Summary
by MITRE
The mptsas_fetch_requests function in hw/scsi/mptsas.c in QEMU (aka Quick Emulator) allows local guest OS administrators to cause a denial of service (infinite loop, and CPU consumption or QEMU process crash) via vectors involving s->state.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-4964 resides within the QEMU virtualization platform's implementation of the mptsas_fetch_requests function located in the hw/scsi/mptsas.c file. This function serves as a critical component in handling SCSI request processing for virtualized storage devices, particularly those utilizing the MegaRAID SCSI controller emulation. The flaw manifests when local guest operating system administrators manipulate specific state variables within the s->state parameter, creating a condition that triggers an infinite loop within the virtualized storage subsystem. This particular vulnerability represents a significant security concern as it allows for a denial of service attack that can consume excessive CPU resources or potentially crash the entire QEMU process, thereby disrupting virtual machine operations and compromising system availability.
The technical implementation of this vulnerability stems from inadequate state validation and error handling within the mptsas_fetch_requests function. When guest administrators manipulate the s->state variable in specific ways, the function fails to properly validate the state transitions, leading to a scenario where the processing loop becomes trapped in an infinite iteration. This condition directly violates the principles of defensive programming and proper state machine implementation as outlined in CWE-691, which addresses insufficient control flow management. The flaw demonstrates a classic example of how improper state handling can lead to resource exhaustion and system instability, particularly within virtualized environments where guest operating systems have elevated privileges.
The operational impact of this vulnerability extends beyond simple service disruption to encompass potential system-wide stability issues within virtualized infrastructures. When exploited, the infinite loop causes continuous CPU consumption that can degrade overall system performance or lead to complete system hang conditions. For enterprise virtualization environments, this vulnerability poses a serious threat as it allows malicious or compromised guest administrators to effectively perform a denial of service attack against the host system, potentially affecting multiple virtual machines running on the same physical host. The vulnerability is particularly concerning in multi-tenant cloud environments where guest isolation is paramount, as it can be used to attack other virtual machines sharing the same hypervisor resources, representing a clear violation of the principle of least privilege and isolation.
Mitigation strategies for CVE-2016-4964 should prioritize immediate patching of affected QEMU versions, as the vulnerability was addressed through proper state validation and loop termination conditions in subsequent releases. Organizations should implement monitoring solutions to detect unusual CPU consumption patterns that might indicate exploitation attempts, while also ensuring proper guest OS privilege controls and isolation mechanisms are in place. The vulnerability highlights the importance of proper input validation and state management in virtualization components, aligning with ATT&CK technique T1499.004 for resource hijacking and T1059.001 for command and scripting interpreter usage. Additionally, implementing network segmentation and access controls to limit guest administrator privileges can serve as effective compensating controls, while regular security assessments of virtualization platforms should include thorough review of state management and error handling mechanisms to prevent similar issues from emerging in the future.