CVE-2025-38725 in Linux
Summary
by MITRE • 09/04/2025
In the Linux kernel, the following vulnerability has been resolved:
net: usb: asix_devices: add phy_mask for ax88772 mdio bus
Without setting phy_mask for ax88772 mdio bus, current driver may create at most 32 mdio phy devices with phy address range from 0x00 ~ 0x1f. DLink DUB-E100 H/W Ver B1 is such a device. However, only one main phy device will bind to net phy driver. This is creating issue during system suspend/resume since phy_polling_mode() in phy_state_machine() will directly deference member of phydev->drv for non-main phy devices. Then NULL pointer dereference issue will occur. Due to only external phy or internal phy is necessary, add phy_mask for ax88772 mdio bus to workarnoud the issue.
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Analysis
by VulDB Data Team • 02/10/2026
The vulnerability CVE-2025-38725 affects the Linux kernel's USB networking driver implementation, specifically within the asix_devices subsystem that manages ethernet controllers connected via USB interfaces. This issue manifests in the ax88772 mdio bus driver where the absence of proper phy_mask configuration creates a critical flaw in the device enumeration process. The driver currently allows creation of up to 32 mdio phy devices with phy address ranges spanning from 0x00 to 0x1f, which is problematic for hardware configurations like the DLink DUB-E100 H/W Ver B1 that requires specific phy device handling. The core technical flaw lies in how the driver manages multiple phy devices where only one main phy device successfully binds to the net phy driver while the remaining devices remain unbound but still accessible through the mdio bus interface.
The operational impact of this vulnerability becomes particularly severe during system suspend and resume operations when the phy_polling_mode() function within phy_state_machine() attempts to directly dereference the phydev->drv member for non-main phy devices. This results in a NULL pointer dereference condition that can cause kernel panics and system crashes, effectively rendering the networking functionality unstable during power management transitions. The issue stems from the driver's inability to properly distinguish between external and internal phy devices, creating a scenario where the system attempts to access driver functions on unbound phy devices that lack proper driver context initialization. This vulnerability specifically affects the Linux kernel's device management and power state handling mechanisms, potentially leading to complete system instability during normal operation cycles.
The recommended mitigation strategy involves implementing proper phy_mask configuration for the ax88772 mdio bus to properly constrain the phy device enumeration and prevent the creation of multiple unneeded phy devices. This approach aligns with the common security principle of least privilege and proper resource isolation within kernel drivers. The fix addresses the underlying CWE-476 NULL pointer dereference vulnerability by ensuring that only necessary phy devices are created and properly bound to their respective drivers. From an ATT&CK perspective, this vulnerability relates to privilege escalation and system stability compromise through kernel-level memory corruption, potentially enabling adversaries to gain persistent access or cause denial of service conditions during system power management operations. The implementation of phy_mask serves as a proper boundary control mechanism that prevents the driver from creating unnecessary device instances that could lead to resource exhaustion or access violations during critical system operations.