CVE-2021-47049 in Linux
Summary
by MITRE • 02/28/2024
In the Linux kernel, the following vulnerability has been resolved:
Drivers: hv: vmbus: Use after free in __vmbus_open()
The "open_info" variable is added to the &vmbus_connection.chn_msg_list, but the error handling frees "open_info" without removing it from the list. This will result in a use after free. First remove it from the list, and then free it.
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Analysis
by VulDB Data Team • 12/09/2024
The vulnerability identified as CVE-2021-47049 represents a critical use-after-free condition within the Linux kernel's Hyper-V vmbus driver implementation. This flaw exists in the __vmbus_open() function where the driver manages communication channels between the host and guest virtual machines. The issue manifests when the driver attempts to handle channel open operations in virtualized environments, specifically affecting systems running the Linux kernel with Hyper-V hypervisor integration. The vulnerability resides in the vmbus subsystem which serves as the communication interface between Hyper-V host and guest operating systems, making it a significant concern for virtualized infrastructures.
The technical implementation flaw occurs due to improper synchronization of memory management operations within the driver's error handling path. When the driver processes channel open requests, it adds an open_info structure to the vmbus_connection.chn_msg_list linked list for tracking purposes. However, during error conditions, the driver frees this open_info structure without first removing it from the linked list. This sequence creates a scenario where the freed memory reference remains accessible in the list structure, leading to potential use-after-free vulnerabilities. The flaw demonstrates poor resource management practices and highlights the importance of maintaining data structure integrity during error recovery operations.
The operational impact of this vulnerability extends beyond simple memory corruption, as it can potentially enable privilege escalation and system instability within virtualized environments. Attackers could exploit this condition to execute arbitrary code with kernel privileges, effectively compromising the security boundary between host and guest systems. The vulnerability affects any Linux system running with Hyper-V integration and is particularly concerning in cloud computing environments where multiple virtual machines share the same physical host. The use-after-free condition could lead to denial of service scenarios or more severe exploitation opportunities depending on the specific memory layout and access patterns. This vulnerability directly relates to CWE-416 which addresses use-after-free conditions, and can be mapped to ATT&CK technique T1068 which covers local privilege escalation through kernel exploits.
Mitigation strategies for CVE-2021-47049 involve applying the official kernel patches released by the Linux kernel development team, which correct the ordering of list removal and memory freeing operations in the __vmbus_open() function. System administrators should prioritize patching affected systems, particularly those running virtualized workloads with Hyper-V integration. Organizations should implement comprehensive monitoring for unusual system behavior or kernel crashes that might indicate exploitation attempts. Additionally, maintaining up-to-date virtualization platforms and ensuring proper isolation between guest operating systems can help reduce the attack surface. The fix ensures that memory management operations follow proper sequence where list entries are removed before memory deallocation, preventing the dangling pointer references that lead to use-after-free conditions. Regular security audits of kernel modules and driver implementations should be conducted to identify similar resource management issues that could present analogous vulnerabilities.