CVE-2026-72113 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
can: bcm: add missing device refcount for CAN filter removal
sashiko-bot remarked a problem with a concurrent device unregistration in isotp.c which also is present in the bcm.c code. A former fix for raw.c commit c275a176e4b6 ("can: raw: add missing refcount for memory leak fix") introduced a netdevice_tracker which solves the issue for bcm.c too.
bcm_release(), bcm_delete_rx_op() and bcm_notifier() relied on dev_get_by_index(ifindex) to re-find the device for an rx_op before unregistering its filter. If a concurrent NETDEV_UNREGISTER has already unlisted the device from the ifindex table, that lookup fails and can_rx_unregister() is silently skipped, leaving a stale CAN filter pointing at the soon-to-be-freed bcm_op/socket.
Hold a netdev_hold()/netdev_put() tracked reference on op->rx_reg_dev from the moment the rx filter is registered in bcm_rx_setup() until it is unregistered in bcm_rx_unreg(), and use that reference directly in bcm_release() and bcm_delete_rx_op() instead of re-looking the device up by ifindex.
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Analysis
by VulDB Data Team • 08/16/2026
The Linux kernel's Controller Area Network (CAN) subsystem contains a critical race condition vulnerability within the Broadcast Management Protocol implementation, specifically affecting the bcm.c module. This issue arises from improper handling of network device references during concurrent operations involving filter removal and device unregistration. The root cause lies in the reliance on dev_get_by_index to locate network devices by their interface index when performing cleanup tasks such as releasing resources or deleting receive operations. While this approach works under normal circumstances, it fails catastrophically if a NETDEV_UNREGISTER event occurs concurrently with these cleanup routines. In such scenarios, the device may have already been removed from the global ifindex table before the lookup is attempted, causing the function to return null and preventing subsequent unregistration of CAN filters.
This failure results in stale pointers remaining within the kernel memory space, pointing toward bcm_op structures or sockets that are subsequently freed due to the ongoing unregistration process. Accessing these dangling references can lead to use-after-free conditions, which represent a severe class of vulnerabilities often categorized under CWE-416: Use After Free. The exploitation potential for such flaws includes arbitrary code execution, kernel panic, or denial of service depending on how an attacker triggers the race condition and manipulates memory contents at the time of access. This vulnerability mirrors similar issues previously identified in isotp.c and raw.c, highlighting a systemic pattern where reference counting mechanisms were insufficiently implemented across different CAN protocol handlers.
The resolution involves introducing proper device refcounting using netdev_hold and netdev_put functions to maintain tracked references throughout the lifecycle of receive operations. Specifically, a netdevice_tracker-based reference is now held on op->rx_reg_dev starting from the moment an rx filter is registered in bcm_rx_setup until it is explicitly unregistered in bcm_rx_unreg. This ensures that even if concurrent device unregistration occurs, the underlying network device structure remains valid and accessible during cleanup operations. By replacing dynamic lookups by interface index with direct usage of these held references, the code eliminates the window where stale pointers could be created due to timing discrepancies between filter removal and device teardown processes.
From a defensive perspective, this fix aligns with industry best practices for managing kernel object lifecycles and mitigating race conditions in network subsystems. It corresponds closely to ATT&CK technique T1059: Command and Scripting Interpreter if considering potential exploitation paths involving script-based attacks targeting vulnerable interfaces, although the primary classification remains within memory safety violations. Security practitioners should ensure that all CAN interface drivers adhere to strict reference counting protocols when handling dynamic device states. Regular auditing of network driver code for similar patterns where dev_get_by_index is used without corresponding hold mechanisms can prevent recurrence of such vulnerabilities across other kernel modules.
Administrators managing systems with active CAN bus configurations must apply the relevant kernel patch immediately upon availability. Given that this vulnerability affects core networking infrastructure, delayed remediation could expose critical industrial control systems or automotive networks to potential compromise through crafted network traffic designed to trigger concurrent unregistration events. Continuous monitoring for unusual kernel behavior related to CAN subsystems and ensuring timely application of security updates remain essential components of maintaining robust cybersecurity posture in environments utilizing Linux-based embedded platforms with CAN capabilities.