CVE-2021-47436 is a vulnerability in the Linux kernel's USB subsystem, specifically within the musb (Mentor USB) driver related to the dsps (Dual-role USB controller) component. The issue arises from an incorrect error handling path introduced by commit 7c75bde329d7, which inverted the order of calls to dsps_setup_optional_vbus_irq() and dsps_create_musb_pdev() without properly updating the error cleanup logic. The dsps_create_musb_pdev() function allocates and registers a platform device that must be unregistered and freed if an error occurs. However, in the flawed code path, this cleanup is missing when dsps_setup_optional_vbus_irq() returns an error, leading to a dangling platform device. This situation can cause a NULL pointer dereference and kernel crash, as observed on the Beagle Bone Black Wireless device running a backported v5.10.70 stable kernel. The root cause is that the platform device remains registered despite the probe failure, and the USB Ethernet gadget driver attempts to use this stale device during boot, triggering the crash. The vulnerability does not appear to be exploitable on the mainline kernel due to differences in the probe behavior but affects certain stable kernel versions with backported patches. The fix involves correcting the error path to ensure proper unregistration of the platform device on failure, preventing the kernel crash and potential system instability. This vulnerability is a logic error in kernel driver resource management rather than a direct security exploit vector but can cause denial of service through kernel crashes.

For European organizations, the primary impact of CVE-2021-47436 is the risk of system instability and denial of service (DoS) on devices running affected Linux kernel versions, particularly embedded systems or specialized hardware like the Beagle Bone Black Wireless that use the musb USB controller driver. This can disrupt operations relying on USB Ethernet gadgets or other USB functionalities tied to the musb driver. While this vulnerability does not directly lead to privilege escalation or data breaches, the resulting kernel crashes can cause downtime, loss of availability, and potential disruption of critical services. Organizations using embedded Linux devices in industrial control systems, IoT deployments, or network appliances that rely on affected kernel versions may experience unexpected reboots or failures. This could impact sectors such as manufacturing, telecommunications, and critical infrastructure where embedded Linux is prevalent. The lack of known exploits in the wild reduces immediate risk, but unpatched systems remain vulnerable to accidental crashes or targeted DoS attempts by adversaries with local access.

European organizations should take the following specific steps to mitigate CVE-2021-47436: 1) Identify all devices and systems running affected Linux kernel versions, especially those using the musb USB controller driver, including embedded devices and IoT hardware. 2) Apply the official Linux kernel patches that fix the error path in the musb_dsps driver as soon as they become available or upgrade to a kernel version where this issue is resolved. 3) For devices where kernel upgrades are not feasible, consider disabling or limiting the use of the musb USB Ethernet gadget functionality if it is not required, to reduce exposure. 4) Implement monitoring for kernel crashes and system instability that could indicate this issue is being triggered. 5) Engage with hardware vendors and embedded system suppliers to ensure they provide updated firmware or kernel versions addressing this vulnerability. 6) For critical infrastructure, establish redundancy and failover mechanisms to minimize impact from potential device crashes. 7) Educate system administrators about the symptoms of this vulnerability and the importance of timely patching in embedded Linux environments.