CVE-2021-44733 in Linux
Summary
by MITRE • 12/22/2021
A use-after-free exists in drivers/tee/tee_shm.c in the TEE subsystem in the Linux kernel through 5.15.11. This occurs because of a race condition in tee_shm_get_from_id during an attempt to free a shared memory object.
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Analysis
by VulDB Data Team • 05/18/2025
The vulnerability described in CVE-2021-44733 represents a critical use-after-free condition within the Trusted Execution Environment (TEE) subsystem of the Linux kernel. This flaw exists in the drivers/tee/tee_shm.c file and affects kernel versions through 5.15.11, making it a widespread concern across numerous production systems. The TEE subsystem provides secure communication channels between trusted and untrusted environments, making this vulnerability particularly dangerous as it could potentially allow attackers to escalate privileges or compromise the security boundaries that the subsystem is designed to maintain.
The technical root cause of this vulnerability stems from a race condition present in the tee_shm_get_from_id function within the TEE shared memory management code. During the process of attempting to free a shared memory object, the system fails to properly synchronize access to the memory structure, creating a window where a freed memory location can be accessed by another thread or process before the memory is completely deallocated. This race condition allows for the possibility of memory corruption, where subsequent operations might write to or read from memory that has already been freed, leading to unpredictable behavior and potential exploitation opportunities.
The operational impact of this vulnerability extends beyond simple memory corruption, as it represents a fundamental flaw in the kernel's memory management and concurrency control mechanisms. When exploited, this use-after-free condition could enable attackers to execute arbitrary code with kernel privileges, potentially leading to complete system compromise. The vulnerability is particularly concerning because it affects the TEE subsystem, which is designed to provide security isolation, making successful exploitation potentially devastating for systems relying on trusted execution environments. Attackers could leverage this flaw to bypass security boundaries, access sensitive data, or establish persistent backdoors within the kernel space.
Mitigation strategies for CVE-2021-44733 should focus on immediate kernel updates to versions that contain the necessary patches addressing the race condition in the TEE subsystem. Organizations should prioritize patching their systems as soon as possible, particularly those running kernel versions between 5.0 and 5.15.11. Additionally, implementing runtime monitoring and intrusion detection systems can help identify potential exploitation attempts, though this represents a reactive approach rather than a preventive solution. The vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions, and could potentially map to ATT&CK technique T1059 for privilege escalation through kernel-level code execution, making it a significant concern for enterprise security teams managing Linux-based infrastructure that relies on TEE capabilities for security isolation.