CVE-2025-38086

In the Linux kernel, the following vulnerability has been resolved:

net: ch9200: fix uninitialised access during mii_nway_restart

In mii_nway_restart() the code attempts to call mii->mdio_read which is ch9200_mdio_read(). ch9200_mdio_read() utilises a local buffer called "buff", which is initialised with control_read(). However "buff" is conditionally initialised inside control_read():

    if (err == size) {
            memcpy(data, buf, size);
    }

If the condition of "err == size" is not met, then "buff" remains uninitialised. Once this happens the uninitialised "buff" is accessed and returned during ch9200_mdio_read():

    return (buff[0] | buff[1] << 8);

The problem stems from the fact that ch9200_mdio_read() ignores the return value of control_read(), leading to uinit-access of "buff".

To fix this we should check the return value of control_read() and return early on error.

This vulnerability is rated as Moderate impact for Red Hat Enterprise Linux because exploitation requires local access or the ability to attach a physical or emulated USB Ethernet adapter to the host system. In typical enterprise server deployments, specialized USB network devices are uncommon, substantially limiting the attack surface. If an attacker attaches a malicious device or triggers an autonegotiation failure on an affected interface, the flaw could result in reading uninitialized kernel memory or unpredictable driver behavior, but does not grant direct remote code execution.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.