CVE-2016-6351 in QEMU
Summary
by MITRE
The esp_do_dma function in hw/scsi/esp.c in QEMU (aka Quick Emulator), when built with ESP/NCR53C9x controller emulation support, allows local guest OS administrators to cause a denial of service (out-of-bounds write and QEMU process crash) or execute arbitrary code on the QEMU host via vectors involving DMA read into ESP command buffer.
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Analysis
by VulDB Data Team • 09/15/2022
The CVE-2016-6351 vulnerability resides within the QEMU virtualization platform's ESP/NCR53C9x controller emulation functionality, specifically in the esp_do_dma function located in hw/scsi/esp.c. This flaw represents a critical security issue that affects virtualized environments where QEMU is configured with SCSI controller emulation capabilities. The vulnerability manifests when guest operating systems with administrative privileges attempt to perform DMA operations through the emulated ESP controller, creating a pathway for privilege escalation and system compromise. The affected component operates at the hardware emulation layer of QEMU, making it particularly dangerous as it can be exploited by attackers who have gained administrative access within a guest operating system.
The technical root cause of this vulnerability stems from inadequate input validation and bounds checking within the esp_do_dma function. When processing DMA read operations into the ESP command buffer, the function fails to properly validate the size and boundaries of data transfers, leading to out-of-bounds memory write operations. This memory corruption occurs because the function does not adequately verify the length of data being transferred from the guest to the host's memory space, allowing maliciously crafted SCSI commands to overwrite adjacent memory locations. The vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and CWE-787, which addresses out-of-bounds write vulnerabilities. The flaw essentially allows an attacker to manipulate memory layout and potentially execute arbitrary code with the privileges of the QEMU process running on the host system.
The operational impact of CVE-2016-6351 extends beyond simple denial of service scenarios, as it enables remote code execution on the host system through a guest-to-host privilege escalation vector. Attackers with administrative access in a guest operating system can exploit this vulnerability to compromise the entire host environment, potentially leading to complete system takeover. The vulnerability affects all QEMU versions that include ESP/NCR53C9x controller emulation support, making it widespread across virtualized infrastructures. The attack requires only local administrative privileges within the guest OS, which significantly reduces the attack surface compared to remote exploitation vectors. This characteristic makes the vulnerability particularly concerning for cloud environments and multi-tenant virtualization platforms where guest isolation is paramount for security. The potential for arbitrary code execution on the host system creates an attack pathway that can be leveraged for data exfiltration, persistence mechanisms, or further lateral movement within the network infrastructure.
Mitigation strategies for CVE-2016-6351 should focus on immediate patching of QEMU installations, with administrators prioritizing updates to versions that contain fixes for the esp_do_dma function. Organizations should also consider disabling ESP/NCR53C9x controller emulation if it is not essential for their virtualized environments, effectively removing the attack surface. Network segmentation and monitoring of virtualization platforms can help detect anomalous behavior that might indicate exploitation attempts. Additionally, implementing strict guest OS privilege controls and regular security audits of virtualized environments can reduce the likelihood of successful exploitation. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and remote code execution, specifically T1068 for local privilege escalation and T1059 for execution of malicious code on the host system. Organizations should also consider implementing virtualization-specific security controls and ensuring that QEMU instances run with minimal required privileges to limit the potential impact of successful exploitation attempts.