CVE-2021-47570 in Linux
Summary
by MITRE • 05/24/2024
In the Linux kernel, the following vulnerability has been resolved:
staging: r8188eu: fix a memory leak in rtw_wx_read32()
Free "ptmp" before returning -EINVAL.
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Analysis
by VulDB Data Team • 08/06/2025
The vulnerability identified as CVE-2021-47570 resides within the Linux kernel's staging driver for the r8188eu wireless network adapter. This specific issue manifests as a memory leak within the rtw_wx_read32() function, which operates within the context of wireless device management and configuration. The r8188eu driver is part of the broader staging subsystem of the Linux kernel, designed to accommodate drivers that are not yet considered stable enough for the mainline kernel but require inclusion for hardware support. The memory leak occurs when the function fails to properly release allocated memory resources before returning an error code, specifically -EINVAL, which indicates an invalid argument error.
The technical flaw stems from improper resource management within the driver's wireless configuration interface. When the rtw_wx_read32() function encounters a condition that warrants returning -EINVAL, it fails to execute the necessary cleanup operation to free the "ptmp" memory pointer that was previously allocated. This memory allocation typically occurs during the processing of wireless configuration commands or queries, where temporary buffers are required to handle data transfers between user space and kernel space. The failure to free this memory results in a gradual accumulation of unreleased memory segments that persist throughout the system's operation, ultimately leading to resource exhaustion and potential system instability.
From an operational perspective, this vulnerability represents a significant concern for systems running Linux kernels with the r8188eu driver, particularly those deployed in environments where wireless connectivity is essential. The memory leak can accumulate over time, especially when the wireless interface experiences frequent configuration operations or error conditions. While the immediate impact may not be catastrophic, prolonged system exposure can lead to degraded performance, memory pressure, and in extreme cases, system crashes or unexpected reboots. The vulnerability affects systems where wireless network configuration is actively managed through the wireless extensions interface, which is common in embedded systems, IoT devices, and various network infrastructure deployments.
The mitigation strategy for CVE-2021-47570 involves applying the kernel patch that ensures proper memory cleanup before returning -EINVAL. This fix aligns with fundamental security principles outlined in the CWE (Common Weakness Enumeration) catalog under CWE-401, which addresses "Improper Release of Memory Before Removing Last Reference" as a critical weakness in software memory management. The solution demonstrates adherence to secure coding practices recommended by the ATT&CK framework's system hardening principles, specifically targeting memory management vulnerabilities that can be exploited to cause resource exhaustion attacks. System administrators should prioritize applying the kernel update that includes this fix, particularly in environments where wireless network interfaces are actively used and where resource constraints are critical. The patch ensures that all allocated memory is properly freed before function exit, maintaining system stability and preventing potential denial-of-service conditions that could arise from progressive memory consumption.
This vulnerability exemplifies the importance of proper resource management in kernel drivers, where memory leaks can have cascading effects on system performance and reliability. The fix demonstrates the critical need for thorough code review and testing of driver components, particularly those handling user-space interactions through wireless configuration interfaces. The resolution addresses a fundamental flaw in the driver's error handling mechanism and reinforces the principle that all allocated resources must be properly released regardless of the execution path taken by the function.