CVE-2025-39985
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk6th percentile - higher than 6% of all known CVEs
Summary
The mcba_usb driver in the Linux kernel lacks the ndo_change_mtu() implementation, allowing an attacker to set an invalid MTU (e.g., 9999) and send a malicious CAN XL frame via a PF_PACKET socket. The frame bypasses standard checks and causes a 247-byte buffer overflow because the driver misinterprets the flags field as data length.
Risk Assessment
An attacker can remotely trigger a kernel buffer overflow, potentially leading to arbitrary code execution or system crash (DoS). The vulnerability affects systems with the mcba_usb driver and access to CAN interfaces.
Recommendation
Immediately update the Linux kernel to a version containing the fix that implements ndo_change_mtu() and limits MTU to CAN_MTU. If updating is not possible, restrict access to CAN interfaces and block PF_PACKET sockets for unprivileged users.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: can: mcba_usb: populate ndo_change_mtu() to prevent buffer overflow Sending an PF_PACKET allows to bypass the CAN framework logic and to directly reach the xmit() function of a CAN driver. The only check which is performed by the PF_PACKET framework is to make sure that skb->len fits the interface's MTU. Unfortunately, because the mcba_usb driver does not populate its net_device_ops->ndo_change_mtu(), it is possible for an attacker to configure an invalid MTU by doing, for example: $ ip link set can0 mtu 9999 After doing so, the attacker could open a PF_PACKET socket using the ETH_P_CANXL protocol: socket(PF_PACKET, SOCK_RAW, htons(ETH_P_CANXL)) to inject a malicious CAN XL frames. For example: struct canxl_frame frame = { .flags = 0xff, .len = 2048, }; The CAN drivers' xmit() function are calling can_dev_dropped_skb() to check that the skb is valid, unfortunately under above conditions, the malicious packet is able to go through can_dev_dropped_skb() checks: 1. the skb->protocol is set to ETH_P_CANXL which is valid (the function does not check the actual device capabilities). 2. the length is a valid CAN XL length. And so, mcba_usb_start_xmit() receives a CAN XL frame which it is not able to correctly handle and will thus misinterpret it as a CAN frame. This can result in a buffer overflow. The driver will consume cf->len as-is with no further checks on these lines: usb_msg.dlc = cf->len; memcpy(usb_msg.data, cf->data, usb_msg.dlc); Here, cf->len corresponds to the flags field of the CAN XL frame. In our previous example, we set canxl_frame->flags to 0xff. Because the maximum expected length is 8, a buffer overflow of 247 bytes occurs! Populate net_device_ops->ndo_change_mtu() to ensure that the interface's MTU can not be set to anything bigger than CAN_MTU. By fixing the root cause, this prevents the buffer overflow.