CVE-2021-3483 in Linux
Summary
by MITRE • 05/17/2021
A flaw was found in the Nosy driver in the Linux kernel. This issue allows a device to be inserted twice into a doubly-linked list, leading to a use-after-free when one of these devices is removed. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability. Versions before kernel 5.12-rc6 are affected
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Analysis
by VulDB Data Team • 05/20/2021
The vulnerability identified as CVE-2021-3483 represents a critical flaw within the Linux kernel's Nosy driver implementation that demonstrates a fundamental failure in memory management and data structure integrity. This issue resides in the kernel's handling of device insertion operations within doubly-linked list data structures, where the flaw manifests as a condition that permits the same device node to be added multiple times to the same linked list structure. The Nosy driver, which typically manages device notifications and monitoring within kernel space, becomes susceptible to this vulnerability due to inadequate validation mechanisms during device registration processes. The flaw specifically affects kernel versions prior to 5.12-rc6, indicating that this represents a relatively recent discovery within the kernel development cycle, suggesting that the vulnerability has been present in production systems for an extended period without detection.
The technical exploitation of this vulnerability occurs through a carefully orchestrated sequence of device insertion operations that bypass normal validation checks. When a device is registered with the Nosy driver, the kernel fails to properly verify whether the device already exists within the doubly-linked list structure before adding it again. This duplication creates a scenario where multiple references point to the same memory location within the list, fundamentally compromising the data structure's integrity. The use-after-free condition emerges when one of these duplicate entries is subsequently removed from the list, leaving the other references pointing to freed memory locations. This creates a dangerous state where any further access to the freed memory can result in arbitrary code execution, memory corruption, or system instability. The vulnerability directly maps to CWE-415, which describes double free conditions, and CWE-416, which addresses use-after-free errors, both of which are classified as critical memory safety issues within the Common Weakness Enumeration framework.
The operational impact of CVE-2021-3483 extends far beyond simple system instability, presenting significant threats to the fundamental security assurances of Linux-based systems. The confidentiality implications arise from the potential for attackers to exploit the use-after-free condition to read sensitive kernel memory contents, potentially extracting cryptographic keys, user credentials, or other confidential data stored in memory. Integrity threats manifest through the possibility of modifying kernel data structures or executing malicious code with elevated privileges, as the vulnerability allows for memory corruption that can be leveraged to gain kernel-level control. System availability is compromised through the potential for denial-of-service conditions that can cause system crashes or reboot cycles, particularly when the vulnerability is triggered during critical device management operations. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1068, which involves local privilege escalation through kernel exploits, and T1499, which encompasses network denial-of-service attacks that can be amplified through kernel-level vulnerabilities.
The mitigation strategy for CVE-2021-3483 requires immediate kernel version updates to 5.12-rc6 or later releases where the vulnerability has been addressed through proper validation of device insertion operations and improved doubly-linked list management. System administrators should prioritize patching critical production environments, particularly those running older kernel versions that remain vulnerable to exploitation. Additional mitigations include implementing kernel lockdown mechanisms and restricting device insertion capabilities where possible, though these approaches represent temporary measures rather than permanent fixes. Security monitoring should focus on detecting anomalous device registration patterns that might indicate exploitation attempts, while also maintaining comprehensive logging of kernel memory operations. The vulnerability highlights the importance of thorough testing of kernel subsystems, particularly those handling dynamic data structures, and demonstrates the critical need for proper input validation in kernel space operations to prevent similar issues from emerging in other subsystems. Organizations should conduct vulnerability assessments to identify systems running affected kernel versions and establish monitoring procedures to detect potential exploitation attempts targeting this specific memory management flaw.