CVE-2021-47571 in Linux
Summary
by MITRE • 05/24/2024
In the Linux kernel, the following vulnerability has been resolved:
staging: rtl8192e: Fix use after free in _rtl92e_pci_disconnect()
The free_rtllib() function frees the "dev" pointer so there is use after free on the next line. Re-arrange things to avoid that.
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Analysis
by VulDB Data Team • 05/24/2024
The vulnerability identified as CVE-2021-47571 represents a critical use-after-free condition within the Linux kernel's staging driver for rtl8192e wireless network adapters. This flaw exists in the _rtl92e_pci_disconnect() function where improper memory management leads to a scenario that violates fundamental security principles of memory safety. The issue occurs when the free_rtllib() function is called, which frees the device pointer, yet subsequent code attempts to reference this already-freed memory location in the next execution line. This represents a classic memory corruption vulnerability that can potentially be exploited by malicious actors to execute arbitrary code or cause system instability.
The technical nature of this vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions in software systems. The flaw demonstrates poor resource management practices where the driver fails to properly sequence memory deallocation and subsequent pointer usage. In the context of the Linux kernel's device driver framework, this represents a failure in proper cleanup procedures during device disconnection events. The rtl8192e driver, which supports Realtek RTL8192E wireless chips, operates within the kernel's staging directory, indicating it's a driver that may not have undergone the full stabilization process of mainstream kernel components, yet still requires robust security measures.
From an operational impact perspective, this vulnerability could allow attackers to exploit the memory corruption during wireless device disconnection scenarios, potentially leading to privilege escalation or system crashes. The attack surface is particularly relevant in environments where wireless network adapters are frequently connected and disconnected, or where malicious actors might attempt to trigger the disconnection routine deliberately. The vulnerability's exploitation potential is enhanced by the fact that it occurs in kernel space, meaning successful exploitation could result in complete system compromise rather than just application-level issues. This aligns with ATT&CK technique T1068 which involves exploiting vulnerabilities in system processes.
The mitigation strategy for this vulnerability involves applying the kernel patch that re-arranges the code execution order to prevent the use-after-free condition. The fix specifically addresses the improper sequencing of memory deallocation and pointer access by ensuring that the device pointer is not referenced after free_rtllib() has been called. System administrators should prioritize updating to kernel versions containing this fix, particularly in environments where wireless network adapters are actively used and where the risk of exploitation is higher. Regular kernel updates and vulnerability assessments should include verification that staging drivers have been properly patched, as these components often receive less rigorous security review compared to core kernel subsystems. The vulnerability demonstrates the importance of thorough code review processes for all kernel components, regardless of their classification or stability status.