CVE-2016-4952 in QEMU
Summary
by MITRE
QEMU (aka Quick Emulator), when built with VMWARE PVSCSI paravirtual SCSI bus emulation support, allows local guest OS administrators to cause a denial of service (out-of-bounds array access) via vectors related to the (1) PVSCSI_CMD_SETUP_RINGS or (2) PVSCSI_CMD_SETUP_MSG_RING SCSI command.
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Analysis
by VulDB Data Team • 09/14/2022
The vulnerability identified as CVE-2016-4952 affects QEMU, a widely used open-source emulator that enables virtualization of various hardware platforms. This issue specifically manifests when QEMU is compiled with VMware PVSCSI paravirtual SCSI bus emulation support, a feature designed to provide optimized storage I/O performance for guest operating systems. The flaw resides in the handling of specific SCSI commands within the PVSCSI emulation layer, creating a critical security gap that can be exploited by malicious actors with administrative privileges within the guest operating system.
The technical implementation of this vulnerability stems from improper bounds checking within the PVSCSI command processing logic. When guest operating systems execute either the PVSCSI_CMD_SETUP_RINGS or PVSCSI_CMD_SETUP_MSG_RING commands, the QEMU emulator fails to validate array indices properly, leading to out-of-bounds memory access patterns. This type of flaw falls under CWE-129, which specifically addresses insufficient bounds checking, and represents a classic buffer overflow condition that can result in system instability. The vulnerability is particularly concerning because it requires only local administrative access within the guest OS, making it accessible to attackers who have already compromised the guest environment.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it can potentially be leveraged to execute arbitrary code or cause complete system crashes within the virtualized environment. An attacker with guest administrator privileges can craft malicious SCSI commands that trigger the out-of-bounds array access, leading to unpredictable behavior including memory corruption, application crashes, or even complete virtual machine compromise. This vulnerability directly aligns with ATT&CK technique T1059, which covers command and scripting interpreter usage, and T1499, covering endpoint disruption, as it enables adversaries to disrupt virtual machine operations and potentially escalate their privileges within the virtualized infrastructure.
Mitigation strategies for CVE-2016-4952 should focus on immediate patching of QEMU installations that include VMware PVSCSI emulation support, as the vulnerability exists in the command processing logic rather than the underlying virtualization framework itself. System administrators should disable PVSCSI emulation in QEMU configurations when it is not strictly required for performance optimization, particularly in environments where guest operating systems cannot be fully trusted. Additionally, implementing proper input validation and bounds checking mechanisms within the virtualization layer can prevent similar vulnerabilities from manifesting in future deployments. The vulnerability demonstrates the importance of thorough code review processes for virtualization components, especially those handling guest-to-host communication protocols, as these interfaces represent prime targets for exploitation within virtualized environments.