The Linux kernel vulnerability CVE-2026-63987 concerns the ethtool coalesce feature where the ethlnl_update_profile() function iterates over the ETHTOOL_A_PROFILE_IRQ_MODERATION nested Netlink attributes using an index 'i' to write new profile data. The index 'i' is not properly bounded, allowing writes beyond the allocated buffer size, which is fixed at NET_DIM_PARAMS_NUM_PROFILES (5 entries). Since Netlink policies do not constrain the number of nested entries, a user-controlled Netlink message can cause out-of-bounds memory writes. This vulnerability has been resolved in the Linux kernel.

The vulnerability allows a user to send a crafted Netlink message with more nested profile entries than the kernel expects, potentially causing out-of-bounds memory writes. This could lead to memory corruption, which might be exploitable for privilege escalation or denial of service. However, no known exploits in the wild have been reported.

A fix for this vulnerability has been implemented in the Linux kernel. Users and administrators should apply the official kernel updates that include this patch. Since this is a kernel-level vulnerability, updating to a patched kernel version is the recommended remediation. Patch status is not explicitly confirmed in the provided data; therefore, check the vendor or Linux kernel advisory for the exact fixed versions and update accordingly.