CVE-2021-46986 is a use-after-free vulnerability in the Linux kernel's USB gadget driver for the DesignWare Core USB3 (dwc3) controller. The vulnerability arises from improper memory management during the removal of the USB gadget device. Specifically, the dwc3_gadget_release() function frees the gadget structure (dwc->gadget) before the endpoints linked to this structure are properly freed. The endpoints are chained via a linked list anchored at dwc->gadget->ep_list. When the gadget structure is freed prematurely, the linked list pointers become dangling, leading to a use-after-free condition when dwc3_gadget_free_endpoints() subsequently attempts to remove endpoints from the list using list_del(). This flaw was identified through Kernel Address Sanitizer (KASAN) testing and can cause kernel panics during device shutdown sequences. The patch to fix this issue involves splitting the usb_del_gadget_udc() call into separate "del" and "put" operations, ensuring that endpoints are freed before the gadget structure itself is released, thereby preventing the dangling pointer dereference. This vulnerability affects Linux kernel versions containing the commit e81a7018d93a7de31a3f121c9a7eecd0a5ec58b0 and related builds. Although no known exploits are reported in the wild, the flaw could be triggered during device removal or shutdown, potentially leading to kernel crashes or memory corruption.

For European organizations, the impact of CVE-2021-46986 primarily concerns systems running Linux kernels with the affected dwc3 USB gadget driver, especially those using embedded devices, IoT gateways, or specialized hardware that rely on USB gadget functionality. Exploitation could lead to denial of service via kernel panic or instability, disrupting critical services or embedded applications. In environments where Linux is used for industrial control systems, telecommunications, or network infrastructure, such instability could cause operational downtime or degraded performance. While direct remote exploitation is unlikely without local access or device interaction, attackers with physical or privileged access could trigger the vulnerability to escalate disruptions. This could be particularly impactful in sectors like manufacturing, healthcare, or transportation where Linux-based embedded systems are common. Additionally, kernel panics could be leveraged as part of a broader attack chain to facilitate privilege escalation or bypass security controls if combined with other vulnerabilities.

European organizations should prioritize updating Linux kernels to versions that include the fix for CVE-2021-46986. Specifically, applying patches that implement the corrected sequence of freeing USB gadget endpoints before releasing the gadget structure is critical. For embedded or IoT devices where kernel updates are less frequent, vendors should be engaged to provide firmware updates or mitigations. System administrators should audit devices using the dwc3 USB gadget driver and assess exposure, especially in environments with USB device removal or shutdown operations. Additionally, enabling kernel hardening features such as KASAN during testing phases can help detect similar memory management issues proactively. Where possible, restrict physical and privileged access to devices to reduce the risk of exploitation. Monitoring system logs for kernel panics related to USB gadget removal can aid in early detection of attempted exploitation or instability caused by this vulnerability.