CVE-2025-39853 in Linux
Summary
by MITRE • 09/19/2025
In the Linux kernel, the following vulnerability has been resolved:
i40e: Fix potential invalid access when MAC list is empty
list_first_entry() never returns NULL - if the list is empty, it still returns a pointer to an invalid object, leading to potential invalid memory access when dereferenced.
Fix this by using list_first_entry_or_null instead of list_first_entry.
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Analysis
by VulDB Data Team • 01/20/2026
The vulnerability identified as CVE-2025-39853 affects the Linux kernel's i40e driver implementation, specifically addressing a critical flaw in memory access handling within network interface card management. This issue manifests when processing MAC address lists in the driver's data structures, where improper handling of empty lists can lead to system instability and potential security implications. The vulnerability resides in the driver's logic for accessing the first entry in a linked list structure, which is fundamental to how the network driver manages MAC address filtering and access control mechanisms.
The technical root cause stems from the incorrect usage of the list_first_entry() kernel macro within the i40e driver code. This macro is designed to retrieve the first entry from a linked list but fails to properly handle the edge case of empty lists. According to the kernel development standards and best practices, list_first_entry() is documented to always return a valid pointer to a list entry structure, even when the list is empty, which results in dereferencing an invalid memory location. This behavior violates the expected contract of list manipulation functions and creates a scenario where subsequent operations on the returned pointer can cause kernel panics, memory corruption, or unauthorized access to system resources. The flaw directly relates to CWE-476 which describes NULL pointer dereference vulnerabilities, though in this case the pointer is not null but points to invalid memory.
The operational impact of this vulnerability extends beyond simple system crashes, potentially enabling privilege escalation or denial of service attacks against systems running affected kernel versions. Network administrators and system operators using Intel Ethernet 400 series network adapters managed by the i40e driver are at risk of experiencing unexpected system failures, particularly during network configuration changes or when MAC address filtering is actively utilized. The vulnerability can be exploited by malicious actors to cause system instability, potentially leading to complete system hangs or reboots that disrupt network services and compromise system availability. This aligns with ATT&CK technique T1499.004 which describes network denial of service attacks, and represents a critical weakness in the kernel's memory management and list handling subsystems.
The fix implemented for CVE-2025-39853 involves replacing the list_first_entry() macro with list_first_entry_or_null() which properly handles the empty list case by returning NULL when no entries exist in the list. This change ensures that subsequent code can properly check for NULL values before attempting memory dereferences, following standard defensive programming practices recommended in kernel security guidelines. The patch demonstrates adherence to the principle of least privilege and proper resource management, where invalid memory access attempts are prevented through proper boundary checking. Organizations should prioritize applying this kernel update to protect against potential exploitation, as the vulnerability affects systems with Intel 400 series network adapters and represents a fundamental flaw in how kernel drivers handle list data structures. The mitigation strategy focuses on updating to the patched kernel version while maintaining awareness of similar patterns in other kernel subsystems that might exhibit the same improper list handling behavior.