CVE-2025-39985
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-10-15

Last updated on: 2025-10-16

Assigner: kernel.org

Description
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.
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Meta Information
Published
2025-10-15
Last Modified
2025-10-16
Generated
2026-05-07
AI Q&A
2025-10-15
EPSS Evaluated
2026-05-05
NVD
CVE-2025-39985
EUVD
EUVD-2025-34587
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel From 5.15.160 (inc) to 5.16 (inc)
Helpful Resources
Exploitability
CWE
CWE Icon
KEV
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CWE ID Description
CWE-UNKNOWN
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability exists in the Linux kernel's mcba_usb CAN driver. The driver does not properly implement the ndo_change_mtu() function, allowing an attacker to set an invalid MTU value (e.g., 9999). This enables the attacker to send malicious CAN XL frames through a PF_PACKET socket that bypass normal CAN framework checks. The mcba_usb driver misinterprets these frames, leading to a buffer overflow because it copies more data than expected into a fixed-size buffer. This buffer overflow can cause memory corruption and potentially allow further exploitation.


How can this vulnerability impact me? :

The vulnerability can lead to a buffer overflow in the mcba_usb CAN driver, which may cause memory corruption. This can result in system instability, crashes, or potentially allow an attacker to execute arbitrary code with kernel privileges. Essentially, it compromises the security and reliability of systems using the affected driver, potentially leading to denial of service or privilege escalation.


How can this vulnerability be detected on my network or system? Can you suggest some commands?

You can detect this vulnerability by checking if the MTU of the mcba_usb CAN interface has been set to an invalid value larger than the CAN_MTU. For example, use the command: ip link show can0 to check the MTU value. Also, monitor for any unusual PF_PACKET socket usage with ETH_P_CANXL protocol, which can be done by inspecting socket creation or network traffic related to CAN XL frames. Specifically, look for commands or processes that execute: ip link set can0 mtu 9999 or similar. Additionally, checking for raw PF_PACKET sockets with ETH_P_CANXL protocol can help identify attempts to exploit this vulnerability.


What immediate steps should I take to mitigate this vulnerability?

The immediate mitigation is to ensure that the mcba_usb driver populates the ndo_change_mtu() operation to prevent setting the MTU to values larger than CAN_MTU. Until a patched kernel is applied, avoid allowing MTU changes on the CAN interface to values larger than CAN_MTU. You can also restrict or monitor the use of PF_PACKET sockets with ETH_P_CANXL protocol to prevent injection of malicious CAN XL frames. Applying the vendor's kernel update that includes the fix is the definitive mitigation.


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