CVE-2026-18415

Overview

Zephyr RTOS network stack for IEEE 802.15.4 allows an out‑of‑bounds write when sending packets via NET_AF_PACKET sockets, potentially corrupting kernel memory. The flaw is triggered by oversized packets that bypass length checks on the transmit path. It can lead to crashes or privilege escalation.

Description

ieee802154_send() in subsys/net/l2/ieee802154/ieee802154.c copies the outgoing packet into a single fixed 125-byte transmit buffer (tx_frame_buf_pool, sized IEEE802154_MTU). In builds with CONFIG_NET_L2_IEEE802154_FRAGMENT enabled (the default whenever CONFIG_NET_6LO is set), the branch taken when 6LoWPAN fragmentation is not required performed an unchecked net_buf_add_mem(frame_buf, pkt_buf->data, pkt_buf->len). The only guard was __ASSERT_NO_MSG() inside net_buf_simple_add(), which is compiled out without CONFIG_ASSERT, so an oversized packet silently overran the frame buffer. The defect is not reachable from the radio: for NET_AF_INET6 packets ieee802154_6lo_encode_pkt() compares the whole packet length against IEEE802154_MTU and takes the fragmentation path when it does not fit, so every buffer copied on the unfragmented branch is within bounds. It is reachable through NET_AF_PACKET sockets bound to an 802.15.4 interface: for NET_SOCK_RAW the 6LoWPAN block is skipped entirely and for NET_SOCK_DGRAM it returns early on the address-family test, leaving no length validation anywhere on the transmit path (net_context_sendto() and net_if_tx() apply none, and pkt_buffer_length() does not clamp the allocation for this L2). An application — or, in a CONFIG_USERSPACE build, an unprivileged application thread using the zsock_socket()/zsock_sendto() syscalls — can therefore drive a supervisor-mode out-of-bounds write of chosen bytes past the 125-byte pool buffer. With the default CONFIG_NET_BUF_FIXED_DATA_SIZE of 128 bytes the overrun is bounded to roughly ll_hdr_len + 3 bytes; with CONFIG_NET_BUF_VARIABLE_DATA_SIZE a single storage buffer can be as large as CONFIG_NET_PKT_BUF_TX_DATA_POOL_SIZE, making the overrun far larger. The consequence is corruption of memory adjacent to the pool, with a crash or further compromise of kernel state as the practical impact. The fix validates ll_hdr_len + net_pkt_get_len(pkt) + authtag_len against IEEE802154_MTU before any copy and adds a tailroom-checking copy_pkt_to_frame() helper that returns -EMSGSIZE instead of overrunning the buffer. The same change also linearizes the whole net_buf chain into one MAC frame, so packet storage boundaries no longer become frame boundaries on the wire.

Impact

The vulnerability permits an attacker to overwrite adjacent memory, causing kernel crashes or enabling arbitrary code execution. Defenders should treat it as a potential privilege escalation vector affecting the integrity and availability of the device.

Remediation

Upgrade to a patched Zephyr release that validates packet length before copying into the 125‑byte transmit buffer. If upgrading is not immediately possible, disable CONFIG_NET_L2_IEEE802154_FRAGMENT or avoid using NET_AF_PACKET sockets on 802.15.4 interfaces. Ensure CONFIG_ASSERT is enabled to surface the issue during development.

Risk context

Severity is medium (CVSS 6.3) with no EPSS data. The risk is moderate; defenders should prioritize patching in production deployments that use the 802.15.4 network stack.

Affected products

• Zephyr RTOS
• Zephyr 802.15.4 stack
• Zephyr 6LoWPAN
• Zephyr net stack