CVE-2020-12464 in Linux
Summary
by MITRE
usb_sg_cancel in drivers/usb/core/message.c in the Linux kernel before 5.6.8 has a use-after-free because a transfer occurs without a reference, aka CID-056ad39ee925.
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Analysis
by VulDB Data Team • 06/04/2024
The vulnerability identified as CVE-2020-12464 represents a critical use-after-free condition within the Linux kernel's USB subsystem, specifically in the usb_sg_cancel function located in drivers/usb/core/message.c. This flaw exists in kernel versions prior to 5.6.8 and stems from an improper handling of USB transfer references during asynchronous I/O operations. The vulnerability manifests when a USB transfer operation is canceled without maintaining proper reference counting, creating a scenario where memory that has been freed can still be accessed by subsequent operations. This type of vulnerability falls under the Common Weakness Enumeration category CWE-416, which specifically addresses use-after-free conditions that occur when a pointer is used after the memory it references has been freed. The issue is particularly concerning within the context of kernel-level operations where such vulnerabilities can lead to arbitrary code execution or system crashes.
The technical implementation of this vulnerability involves the USB scatter-gather (sg) interface that allows userspace applications to perform asynchronous I/O operations on USB devices. When a USB transfer is initiated through this interface, the kernel maintains internal data structures to track the operation's state and manage memory allocations. The usb_sg_cancel function is responsible for canceling these ongoing transfers, but due to insufficient reference management, it can proceed with cancellation even when the underlying transfer structure has already been freed by another code path. This race condition occurs because the function does not properly verify that the transfer reference remains valid before proceeding with cleanup operations, leading to a situation where freed memory is accessed during the cancellation process. The flaw is particularly dangerous because it can be exploited by malicious users to gain elevated privileges or cause system instability through controlled memory access patterns.
The operational impact of CVE-2020-12464 extends beyond simple system crashes to potentially enable privilege escalation attacks within the Linux kernel environment. Attackers who can trigger the specific conditions leading to this vulnerability may be able to execute arbitrary code with kernel-level privileges, effectively compromising the entire system. This risk is particularly elevated in environments where USB devices are frequently used or where users have the ability to connect untrusted USB hardware, as these scenarios provide multiple attack vectors for exploitation. The vulnerability affects all Linux kernel versions prior to 5.6.8, making it widespread across numerous production systems and embedded devices that rely on older kernel versions. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and kernel exploitation, specifically targeting the kernel's USB subsystem as a means to achieve elevated system access.
Mitigation strategies for CVE-2020-12464 primarily focus on kernel version upgrades to 5.6.8 or later, which contain the necessary patches to address the reference counting issue in the usb_sg_cancel function. System administrators should prioritize patching affected systems, particularly those handling USB I/O operations or running in environments where USB device connectivity is common. Additionally, implementing proper USB device access controls and limiting user privileges for USB operations can reduce the attack surface. Organizations should also consider monitoring for suspicious USB device connections and unusual kernel memory access patterns that might indicate exploitation attempts. The patch implemented in kernel 5.6.8 addresses the root cause by ensuring proper reference counting during transfer cancellation operations, preventing the use-after-free scenario that leads to memory corruption. Security teams should also implement regular vulnerability assessments to identify systems running affected kernel versions and establish processes for rapid patch deployment across their infrastructure.