CVE-2026-99198 in Linux
Summary
by MITRE • 10/28/2026
In the Linux kernel, the following vulnerability has been resolved:
net: ethernet: actions: Move setting of netops to fix crash
owl_emac_probe() calls owl_emac_phy_init(), which connects the PHY, before netdev->netdev_ops is assigned. phy_attach_direct() -> phy_link_topo_add_phy() reads dev->netdev_ops through netdev_need_ops_lock() since the commit in question, so probing crashes with a NULL pointer dereference when CONFIG_NET_SHAPER is enabled.
Assign netdev_ops before the PHY attach, as was done for emac in commit 7c9f391ec89c ("net: emac: move setting of netops to fix crash").
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Analysis
by VulDB Data Team • 10/28/2026
The identified vulnerability represents a critical NULL pointer dereference within the Linux kernel network subsystem, specifically affecting the Actions Semiconductor Owl Ethernet MAC driver. This flaw arises from an incorrect initialization sequence during device probing, where the PHY layer is attached before the core network operations structure is properly assigned to the net_device instance. The root cause lies in the function owl_emac_probe(), which invokes owl_emac_phy_init() to establish a connection with the physical layer interface prior to populating the dev->netdev_ops pointer. This ordering becomes problematic when specific kernel configuration options, particularly CONFIG_NET_SHAPER, are enabled, as this feature introduces additional dependencies that require access to network device operations during PHY initialization routines.
The technical mechanism of the crash involves the phy_attach_direct() function, which subsequently calls phy_link_topo_add_phy(). Within this chain, the code attempts to determine if locking is required for netdev operations by invoking netdev_need_ops_lock(). This helper function directly accesses dev->netdev_ops to verify its validity. Because the driver had not yet assigned a valid structure to this pointer at the time of execution, the kernel encounters a NULL reference. In modern Linux kernels, accessing a NULL pointer in such contexts typically results in an immediate panic or crash, rendering the system unstable and potentially causing a denial of service for any services relying on that network interface or the host itself if it is a critical node.
This issue aligns with CWE-476, which describes a NULL Pointer Dereference vulnerability. The error occurs because software fails to check whether a pointer value is null before using it, leading to unexpected termination or execution of unintended code paths. From an offensive security perspective, this flaw can be mapped to the ATT&CK technique T1595.002, Active Scanning: Vulnerability Scanning, as attackers could potentially use such instability to disrupt availability during reconnaissance phases. However, given that it is a local kernel crash triggered by driver initialization rather than remote exploitation, its primary impact is on system reliability and integrity rather than direct data exfiltration or privilege escalation in most standard configurations.
The operational impact of this vulnerability is primarily centered around system stability and service continuity. When the affected network interface is initialized, whether during boot-up or module loading, the kernel will crash due to the invalid memory access. This prevents the network device from coming online, effectively causing a denial of service for that specific hardware component. In embedded systems or specialized networking equipment where Actions Semiconductor chips are commonly used, this could lead to complete system failure if the root filesystem or critical management interfaces reside on such devices. The vulnerability is conditional upon CONFIG_NET_SHAPER being enabled, which limits its exposure but does not diminish its severity when active.
The resolution involves reordering the initialization steps within the owl_emac_probe() function to ensure that netdev->netdev_ops is assigned before any calls are made to PHY attachment functions like phy_attach_direct(). This approach mirrors a previous fix applied to the emac driver in commit 7c9f391ec89c, establishing consistency across similar Ethernet MAC drivers. By ensuring that all necessary data structures and operation vectors are initialized prior to interacting with dependent subsystems, the kernel avoids accessing uninitialized memory regions.
To mitigate this risk, system administrators and developers should ensure they apply the latest available patches for their Linux distribution or embedded OS build. For those maintaining custom kernels, it is imperative to verify that the driver initialization sequence adheres to the corrected order where netdev_ops assignment precedes PHY layer interactions. Additionally, enabling kernel hardening features such as CONFIG_DEBUG_NULL_PTR_DEREF can help detect similar issues during development and testing phases before deployment. Regularly updating drivers and monitoring for new CVEs related to network subsystem stability is essential for maintaining robust infrastructure security posture against both accidental crashes and potential exploitation vectors that leverage instability.