CVE-2025-38725

What it actually does

Missing phy_mask on ax88772 MDIO bus allows creation of up to 32 PHY devices; only the main PHY binds to a driver, so phy_polling_mode() in phy_state_machine() dereferences phydev->drv on non-main devices, producing a NULL pointer dereference during suspend/resume.

Why it matters to the business

Systems using affected AX88772-based USB Ethernet adapters can experience kernel crashes on every suspend/resume cycle, causing unplanned downtime, interrupted network connectivity, and potential loss of unsaved work.

How an attack unfolds

An attacker with local user privileges triggers a suspend/resume cycle on a system equipped with a vulnerable D-Link DUB-E100 or similar AX88772 adapter; the kernel enters phy_state_machine() for phantom PHY devices, dereferences a NULL drv pointer, and panics.

How to fix it

Upgrade the Linux kernel to the commit 75947d3200de98a9ded9ad8972e02f1a177097fe (or later stable release containing the phy_mask addition for ax88772). Rebuild and reboot with the patched kernel; test suspend/resume with the affected adapter.

How to confirm the fix worked

Confirm the running kernel contains commit 75947d3200de98a9ded9ad8972e02f1a177097fe via git log or uname -a; attach the adapter, perform multiple suspend/resume cycles, and verify no NULL pointer dereference occurs in dmesg.

Typical attack path

1. Obtain local shell or user session on target Linux system
2. Ensure AX88772 USB Ethernet adapter is attached and bound by asix driver
3. Initiate system suspend (echo mem > /sys/power/state or lid close)
4. Resume the system
5. Kernel oops/panic occurs in phy_state_machine

How to detect it

Search kernel logs (dmesg, /var/log/kern.log, journalctl) for NULL pointer dereference, phy_state_machine, phy_polling_mode, and asix_devices entries around suspend/resume timestamps; correlate with USB device attach events for AX88772.

• NULL pointer dereference
• phy_state_machine
• phy_polling_mode
• asix_devices
• ax88772

What your security team should do

• Apply the referenced kernel commit to all affected distributions within the next patch window
• Prioritize systems that routinely use AX88772 USB Ethernet adapters or perform frequent suspend/resume
• Add kernel oops monitoring for phy_state_machine and asix_devices to existing alerting
• Disable unused USB Ethernet adapters via udev rules until patches are deployed