CVE-2016-5238 in QEMU
Summary
by MITRE
The get_cmd function in hw/scsi/esp.c in QEMU might allow local guest OS administrators to cause a denial of service (out-of-bounds write and QEMU process crash) via vectors related to reading from the information transfer buffer in non-DMA mode.
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Analysis
by VulDB Data Team • 08/23/2022
The vulnerability identified as CVE-2016-5238 resides within the QEMU hypervisor's implementation of SCSI command handling, specifically in the get_cmd function located in hw/scsi/esp.c. This flaw represents a critical security issue that can be exploited by local guest operating system administrators to execute a denial of service attack against the host system running QEMU. The vulnerability occurs in the context of SCSI controller emulation where QEMU simulates hardware components for virtualized environments, making it particularly dangerous in cloud computing and virtualization scenarios where multiple tenants share underlying infrastructure.
The technical root cause of this vulnerability stems from improper bounds checking within the SCSI command processing logic when operating in non-DMA mode. The get_cmd function fails to validate the size of data being read from the information transfer buffer, leading to an out-of-bounds write condition. This memory corruption occurs when guest operating systems attempt to execute SCSI commands that manipulate the buffer size beyond allocated boundaries. The flaw specifically manifests when the virtual SCSI controller processes commands that involve reading data from the transfer buffer without adequate validation of buffer limits, resulting in memory corruption that ultimately crashes the QEMU process.
From an operational impact perspective, this vulnerability creates significant risks for virtualized environments where guest operating systems have administrative privileges. Local guest administrators can exploit this flaw to crash the QEMU hypervisor process, effectively causing a denial of service that impacts not only the compromised virtual machine but potentially other virtual machines running on the same host. The attack vector is particularly concerning because it requires only local administrative access within the guest OS, making it accessible to malicious insiders or attackers who have gained administrative privileges within a virtual machine. This vulnerability directly relates to CWE-121, which describes heap-based buffer overflow conditions, and can be categorized under ATT&CK technique T1499.1 for endpoint denial of service attacks targeting hypervisor components.
The exploitation of this vulnerability demonstrates the critical importance of input validation in virtualization software components. When guest operating systems can manipulate the virtualized hardware through legitimate SCSI commands, the hypervisor's memory safety mechanisms become insufficient to prevent malicious data manipulation. This flaw highlights the need for robust bounds checking in all hardware emulation components, particularly those handling data transfer operations that involve buffer management. The out-of-bounds write condition can potentially be extended to more severe attacks if combined with other vulnerabilities or if the memory corruption can be leveraged for privilege escalation within the hypervisor environment. Organizations utilizing QEMU-based virtualization platforms should immediately implement patches addressing this vulnerability and consider additional security measures such as guest operating system hardening, monitoring for unusual process crashes, and implementing proper access controls to limit guest administrative privileges. The vulnerability underscores the necessity of comprehensive security testing for virtualization components and proper adherence to secure coding practices that prevent buffer overflows and memory corruption issues in hypervisor implementations.