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CVE-2025-39986 Affecting kernel-syms package, versions <6.4.0-150600.23.78.1

Severity

 Recommended
0.0
medium
0
10

Based on SUSE Linux Enterprise Server security rating.

Threat Intelligence

EPSS
0.04% (13th percentile)

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  • Snyk IDSNYK-SLES156-KERNELSYMS-14071766
  • published20 Nov 2025
  • disclosed19 Nov 2025
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Introduced: 19 Nov 2025

NewCVE-2025-39986  (opens in a new tab)

How to fix?

Upgrade SLES:15.6 kernel-syms to version 6.4.0-150600.23.78.1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-syms package and not the kernel-syms package as distributed by SLES. See How to fix? for SLES:15.6 relevant fixed versions and status.

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-&gt;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 &lt; dlc; i++)
    writel(cf-&gt;data[i], priv-&gt;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.

CVSS Base Scores

version 3.1