In the Linux kernel, the following vulnerability has been resolved: ipv4: do not warn on route notification size race Commit 680aea08e78c ("net:… (CVE-2026-99071)

The vulnerability concerns the Linux kernel's IPv4 route notification mechanism. Commit 680aea08e78c introduced asynchronous notifications for fib hardware flag changes. The function fib_alias_hw_flags_set() sizes a socket buffer (skb) with fib_nlmsg_size() and later fills it with fib_dump_info() while holding only RCU. When nexthop compatibility mode is enabled, concurrent replacements can cause the group size to grow between these snapshots. This can cause fib_dump_info() to return -EMSGSIZE legitimately, which previously triggered a warning that was not indicative of a sizing bug. The fix removes this warning while retaining the existing error path that frees the skb and reports errors to listeners.

The impact is limited to misleading warnings being generated in the kernel logs due to legitimate size errors during asynchronous route notifications. There is no indication that this causes functional disruption, security bypass, or exploitation. The fix improves kernel stability and log accuracy by removing unnecessary warnings.

A fix has been implemented in the Linux kernel to remove the misleading warning. Users should update to the fixed kernel version containing commit 680aea08e78c or later. No additional mitigation is required as the existing error handling remains intact.