CVE-2021-47457 is a vulnerability identified in the Linux kernel's CAN (Controller Area Network) protocol stack, specifically within the ISO-TP (ISO 15765-2) implementation. The issue arises in the isotp_sendmsg() function, which is responsible for sending messages over the ISO-TP layer. The vulnerability stems from the use of wait_event_interruptible() to wait for the completion of message transmission without properly checking its return value. wait_event_interruptible() can be interrupted by signals, and failure to verify its result means that the transmission buffer (TX buffer) may be accessed concurrently by multiple processes. This concurrent access leads to race conditions where later processes interfere with earlier ones, potentially causing data corruption or kernel instability. The problem was initially reported by syzbot, an automated kernel fuzzing tool, which detected a warning related to the isotp_tx_timer_handler indicating improper synchronization and buffer access. The patch for this vulnerability involves adding a proper check of the wait_event_interruptible() return value in isotp_sendmsg() to ensure that interrupted waits do not lead to multiple accessors on the TX buffer. This fix prevents race conditions and ensures the integrity of CAN message transmissions over ISO-TP in the Linux kernel. The vulnerability affects Linux kernel versions prior to the patch and is relevant to systems using the CAN protocol stack, which is commonly employed in automotive, industrial control, and embedded systems. No known exploits are currently reported in the wild, and the vulnerability does not have an assigned CVSS score at this time.

For European organizations, the impact of CVE-2021-47457 depends largely on their use of Linux-based systems that implement the CAN protocol stack, particularly in automotive, industrial automation, and embedded device contexts. The vulnerability could lead to kernel instability, data corruption, or denial of service on affected systems due to race conditions in the CAN ISO-TP transmission buffer. This may disrupt critical communications in automotive ECUs (Electronic Control Units), industrial machinery, or IoT devices that rely on CAN for real-time messaging. In sectors such as automotive manufacturing, transportation, and critical infrastructure, such disruptions could cause operational downtime, safety risks, or loss of data integrity. Although no active exploits are known, the vulnerability represents a risk for organizations deploying Linux kernels with vulnerable versions in environments where CAN communication is essential. The potential for denial of service or unpredictable behavior in embedded systems could have safety and reliability implications, especially in safety-critical applications prevalent in Europe’s automotive and industrial sectors.

European organizations should take the following specific mitigation steps: 1) Identify all Linux systems running kernels that include the CAN ISO-TP stack, especially those used in automotive, industrial control, or embedded environments. 2) Apply the official Linux kernel patches that add the necessary wait_event_interruptible() result checks in isotp_sendmsg() as soon as they become available, or upgrade to a kernel version that includes this fix. 3) For embedded or custom Linux distributions, coordinate with vendors or internal development teams to backport the patch if upgrading the entire kernel is not feasible. 4) Implement monitoring for kernel warnings or anomalies related to CAN communication, such as messages from isotp_tx_timer_handler, to detect potential exploitation attempts or instability. 5) Conduct thorough testing of CAN communication functionality after patching to ensure no regression or new issues arise. 6) For critical systems, consider network segmentation or isolation of CAN-enabled devices to limit exposure. 7) Maintain up-to-date inventories of devices using CAN and ensure firmware and kernel updates are part of regular maintenance cycles. These steps go beyond generic advice by focusing on the specific affected subsystem and operational contexts relevant to European industries.