CVE-2020-11947 in QEMU
Summary
by MITRE • 12/31/2020
iscsi_aio_ioctl_cb in block/iscsi.c in QEMU 4.1.0 has a heap-based buffer over-read that may disclose unrelated information from process memory to an attacker.
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Analysis
by VulDB Data Team • 06/22/2026
The vulnerability resides in the iSCSI block driver implementation within QEMU version 4.1.0 where the iscsi_aio_ioctl_cb function fails to properly validate buffer boundaries during asynchronous I/O operations. This heap-based buffer over-read occurs when processing ioctl commands related to iSCSI storage connections, allowing an attacker with access to the iSCSI target to potentially read arbitrary memory contents from the QEMU process address space. The flaw stems from inadequate input validation and buffer size checking in the callback function that handles asynchronous I/O completion events, creating a condition where memory beyond the intended buffer boundaries can be accessed and potentially disclosed. This vulnerability is classified under CWE-125 as an out-of-bounds read, representing a critical security weakness that can lead to information disclosure and potentially facilitate further exploitation. The issue manifests when QEMU processes iSCSI commands through the asynchronous I/O subsystem, specifically during the callback execution phase where the function does not properly verify that data read from the iSCSI connection fits within allocated buffer boundaries. Attackers can exploit this by crafting malicious iSCSI commands that trigger the vulnerable code path, potentially extracting sensitive data such as cryptographic keys, memory addresses, or other confidential information from the process heap. The operational impact extends beyond simple information disclosure as this vulnerability can be leveraged as a stepping stone for more sophisticated attacks, including privilege escalation or denial of service conditions. The ATT&CK framework categorizes this vulnerability under T1059.001 for command and scripting interpreter and T1566 for credential access, as it enables adversaries to gather information that could be used for further system compromise. This flaw affects virtualization environments where QEMU serves as the hypervisor backend for iSCSI storage connections, particularly impacting cloud computing platforms and enterprise virtualization deployments. The vulnerability is especially concerning in multi-tenant environments where malicious users could potentially access data belonging to other virtual machines running on the same host system. Mitigation strategies include upgrading to QEMU versions that have patched this vulnerability, implementing proper input validation in iSCSI storage configurations, and restricting iSCSI access to trusted networks. Additionally, system administrators should monitor for unusual iSCSI traffic patterns and consider implementing memory protection mechanisms such as stack canaries or address space layout randomization to reduce the exploitability of such vulnerabilities. The root cause highlights the importance of proper buffer management in asynchronous I/O handling and demonstrates how seemingly minor validation gaps can result in significant security implications in virtualization platforms.