CVE-2026-64120 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
net: ethtool: fix NULL pointer dereference in phy_reply_size
In phy_prepare_data(), several strings such as 'name', 'drvname', 'upstream_sfp_name', and 'downstream_sfp_name' are allocated using kstrdup(). However, these allocations were not checked for failure.
If kstrdup() fails for 'name', it returns NULL while the function continues. This leads to a kernel NULL pointer dereference and panic later in phy_reply_size() when it unconditionally calls strlen() on the NULL pointer.
While other strings like 'upstream_sfp_name' might be checked before access in certain code paths, failing to handle these allocations consistently can lead to incomplete data reporting or hidden bugs.
Fix this by adding proper NULL checks for all kstrdup() calls in phy_prepare_data() and implement a centralized error handling path using goto labels to ensure all previously allocated resources are freed on failure.
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Analysis
by VulDB Data Team • 07/19/2026
This vulnerability exists within the linux kernel's ethernet driver subsystem, specifically in the ethtool interface implementation where the phy_prepare_data() function handles preparation of physical layer device information for reporting. The flaw stems from inconsistent error handling practices during memory allocation operations that can lead to system crashes and potential security implications. When the kernel attempts to duplicate strings using kstrdup() for device identification fields including 'name', 'drvname', 'upstream_sfp_name', and 'downstream_sfp_name', it fails to validate whether these allocations succeed. This represents a classic null pointer dereference vulnerability that can be exploited to cause denial of service conditions or potentially enable privilege escalation attacks depending on the execution context.
The technical implementation flaw occurs because kstrdup() can return NULL when memory allocation fails, yet the phy_prepare_data() function continues execution without checking for this condition. When 'name' allocation specifically fails and returns NULL, subsequent code paths in phy_reply_size() unconditionally invoke strlen() on this null pointer, resulting in immediate kernel panic. This type of vulnerability maps directly to CWE-476 which defines null pointer dereference conditions, and the inconsistency in handling different string allocations creates a subtle but critical security boundary issue. The vulnerability demonstrates poor defensive programming practices where error conditions are not properly propagated through the call stack.
The operational impact of this vulnerability extends beyond simple system crashes as it can affect network availability and potentially provide attackers with opportunities to exploit the kernel's memory management subsystem. When a device driver encounters allocation failures during normal operation, especially under resource-constrained conditions, the system may become unstable or unresponsive. This type of panic condition directly violates the principle of graceful degradation that security-conscious systems should maintain, as it can be triggered by malicious input or simply by resource exhaustion scenarios. The vulnerability affects all systems running affected kernel versions where ethtool operations are performed on physical layer devices.
The fix for this vulnerability requires implementing comprehensive error handling mechanisms throughout the phy_prepare_data() function. Proper solution involves adding explicit NULL checks after each kstrdup() call to ensure that memory allocation failures are detected and handled appropriately. The recommended approach utilizes centralized error handling through goto labels to provide a clean resource cleanup mechanism when allocation failures occur, ensuring all previously allocated resources are properly freed before returning from the function. This approach aligns with ATT&CK technique T1499.004 which involves resource exhaustion attacks, and follows secure coding practices that prevent information disclosure and system instability. The fix should also consider implementing proper logging of allocation failures to aid in debugging and monitoring for potential exploitation attempts.