CVE-2016-4439 in QEMU
Summary
by MITRE
The esp_reg_write function in hw/scsi/esp.c in the 53C9X Fast SCSI Controller (FSC) support in QEMU does not properly check command buffer length, which allows local guest OS administrators to cause a denial of service (out-of-bounds write and QEMU process crash) or potentially execute arbitrary code on the QEMU host via unspecified vectors.
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Analysis
by VulDB Data Team • 08/21/2022
The vulnerability identified as CVE-2016-4439 resides within the QEMU virtualization platform's implementation of the 53C9X Fast SCSI Controller hardware emulation. This flaw specifically affects the esp_reg_write function located in the hw/scsi/esp.c file, which handles register writes for the FSC controller. The issue stems from inadequate validation of command buffer lengths during SCSI command processing, creating a critical security gap that can be exploited by malicious actors within the guest operating system environment.
The technical root cause of this vulnerability manifests as a classic buffer overflow condition where the esp_reg_write function fails to properly validate the length of command buffers before processing them. This oversight allows an attacker with administrative privileges within the guest OS to craft malicious SCSI commands that exceed the allocated buffer boundaries. The vulnerability operates under CWE-121, which classifies buffer overflow conditions that occur when insufficient bounds checking is performed during data processing operations. When the function processes these malformed commands, it can write data beyond the intended buffer limits, leading to unpredictable behavior that manifests as either denial of service through process crashes or potential code execution on the host system.
The operational impact of this vulnerability extends beyond simple system instability, as it represents a significant escalation path from guest-level privilege to host-level compromise. Local guest OS administrators can leverage this flaw to either crash the QEMU process and thereby deny service to legitimate users or potentially execute arbitrary code with the privileges of the QEMU process running on the host. This creates a serious risk in multi-tenant virtualization environments where guest administrators might attempt to compromise other virtual machines or the host system itself. The vulnerability's potential for arbitrary code execution places it within ATT&CK matrix technique T1059, which covers command and scripting interpreter usage, and T1068, which addresses exploit for privilege escalation.
Mitigation strategies for CVE-2016-4439 should focus on immediate patching of affected QEMU versions, as the vulnerability was addressed through proper bounds checking implementation in subsequent releases. Organizations should implement strict access controls and privilege separation within virtualized environments, limiting guest administrative capabilities to reduce exploitation risk. Network segmentation and monitoring solutions should be deployed to detect anomalous SCSI command patterns that might indicate exploitation attempts. Additionally, virtualization administrators should regularly audit their QEMU configurations and ensure that all system components are updated to the latest secure versions, as this vulnerability demonstrates the critical importance of maintaining up-to-date virtualization infrastructure to prevent privilege escalation attacks that can compromise entire host systems.