CVE-2016-5126 in QEMU
Summary
by MITRE
Heap-based buffer overflow in the iscsi_aio_ioctl function in block/iscsi.c in QEMU allows local OS guest users to cause a denial of service (QEMU process crash) or possibly execute arbitrary code via a crafted iSCSI asynchronous I/O ioctl call.
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Analysis
by VulDB Data Team • 08/22/2022
The vulnerability identified as CVE-2016-5126 represents a critical heap-based buffer overflow within the QEMU virtualization platform's iSCSI implementation. This flaw exists in the iscsi_aio_ioctl function located in block/iscsi.c, which handles asynchronous I/O operations for iSCSI storage connections. The vulnerability specifically affects local operating system users within guest virtual machines who can leverage crafted iSCSI asynchronous I/O ioctl calls to exploit the buffer overflow condition. The technical nature of this vulnerability places it under CWE-121, which describes heap-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent memory locations. The flaw stems from inadequate input validation and memory management within the iSCSI subsystem that processes ioctl commands, creating a pathway for malicious data to exceed allocated buffer boundaries.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to potentially enable arbitrary code execution within the QEMU process context. When a guest user crafts a malicious iSCSI async I/O ioctl call, the overflow can corrupt heap memory structures, leading to unpredictable behavior including process crashes or more severe exploitation opportunities. The vulnerability's classification aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as it enables potential code execution within the host system through guest-to-host privilege escalation. Attackers exploiting this vulnerability can leverage the QEMU process privileges to execute malicious code, potentially compromising the entire host system or other virtual machines running on the same host. The heap overflow condition allows for memory corruption that could be manipulated to overwrite function pointers, return addresses, or other critical control structures, providing a pathway for privilege escalation.
Mitigation strategies for CVE-2016-5126 should prioritize immediate patching of affected QEMU versions to address the buffer overflow in the iSCSI implementation. Organizations should implement strict input validation and bounds checking within all iSCSI-related components, particularly focusing on the ioctl handling mechanisms that process asynchronous I/O operations. Network segmentation and access controls should limit guest VM access to iSCSI storage subsystems, reducing the attack surface for potential exploitation. The implementation of memory protection mechanisms such as stack canaries, address space layout randomization, and heap hardening techniques can provide additional defense-in-depth measures. Security monitoring should include detection of unusual iSCSI ioctl patterns and memory access anomalies that could indicate exploitation attempts. System administrators should also consider disabling unnecessary iSCSI functionality in virtual machine configurations and implement regular vulnerability assessments to identify similar memory corruption issues within virtualization platforms. The vulnerability highlights the importance of secure coding practices in virtualization environments and demonstrates how guest operating system users can potentially escalate privileges through host-level vulnerabilities in hypervisor components.