CVE-2025-39986
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: sun4i_can: 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 sun4i_can 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, sun4ican_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 this line: dlc = cf->len; 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 a couple line below when doing: for (i = 0; i < dlc; i++) writel(cf->data[i], priv->base + (dreg + i * 4)); 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-2025-39986
EUVD
EUVD-2025-34586
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
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KEV
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CWE ID Description
CWE-UNKNOWN
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AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability exists in the Linux kernel's sun4i_can driver. The driver does not properly implement the ndo_change_mtu() operation, allowing an attacker to set an invalid MTU value (e.g., 9999) on the CAN interface. By doing so, the attacker can open a PF_PACKET socket with the ETH_P_CANXL protocol and inject malicious CAN XL frames. The driver misinterprets these frames due to insufficient validation, leading to a buffer overflow when processing the frame's length field. This occurs because the driver uses the flags field as a length without proper checks, causing memory corruption.


How can this vulnerability impact me? :

This vulnerability can lead to a buffer overflow in the sun4i_can driver, which may allow an attacker to execute arbitrary code, cause a denial of service (system crash), or compromise the integrity and stability of the affected system. Since the attacker can inject malicious CAN XL frames directly, it could be exploited remotely or locally to disrupt system operations or gain elevated privileges.


What immediate steps should I take to mitigate this vulnerability?

The immediate mitigation step is to ensure that the net_device_ops->ndo_change_mtu() is populated for the sun4i_can driver to prevent setting an invalid MTU larger than CAN_MTU. This prevents attackers from configuring an invalid MTU and injecting malicious CAN XL frames that cause buffer overflow. Until a patch is applied, avoid allowing MTU changes on can interfaces to values larger than CAN_MTU.


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