In the Linux kernel, the following vulnerability has been resolved: fou: reject omitted FOU_ATTR_IPPROTO on FOU_ENCAP_DIRECT Commit 7a9bc9e3f423… (CVE-2026-98541)

The Linux kernel fou module's netlink interface accepts an optional attribute FOU_ATTR_IPPROTO. When creating a FOU_ENCAP_DIRECT socket via FOU_CMD_ADD, omitting this attribute caused the kernel to default the protocol to 0. This led to fou_udp_recv() returning 0, which signals the UDP tunnel layer that the packet was consumed without freeing it, resulting in a leak of sk_buff memory buffers. The patch enforces rejection of FOU_ENCAP_DIRECT socket creation when FOU_ATTR_IPPROTO is omitted, returning -EINVAL to prevent the leak. This fix preserves normal operation of other commands like FOU_CMD_DEL and FOU_CMD_GET.

Exploitation of this vulnerability causes a memory leak in the kernel's network stack, specifically leaking sk_buff structures for each UDP packet received on the affected socket. This can lead to increased kernel memory usage and potential resource exhaustion over time. There is no indication of privilege escalation or remote code execution from the provided data.

A patch has been applied to the Linux kernel that rejects creation of FOU_ENCAP_DIRECT sockets without the FOU_ATTR_IPPROTO attribute, returning an error and preventing the memory leak. Users should update to a kernel version that includes this fix. No other mitigation actions are indicated or necessary.