CVE-2026-18417: zephyr Vulnerability (CVSS 6.5)

Description

The native BSD-socket layer recorded a pending asynchronous socket error by type-punning it into struct net_context's void user_data field (ctx->user_data = INT_TO_POINTER(-status) in zsock_accepted_cb(), zsock_received_cb(), zsock_connected_cb() and zsock_close_ctx() in subsys/net/lib/sockets/sockets_inet.c), reading it back with POINTER_TO_INT(). That same field is owned by the network stack for listening TCP contexts: net_tcp_accept() stores the parent context pointer there and the TCP core passes it back to the registered accept callback. A failed accept therefore left a small integer (an errno value) where the stack expected a struct net_context . When the network interface carrying a listening TCP socket goes down, close_tcp_conn() in subsys/net/ip/tcp.c invokes the accept callback with -ENETDOWN and the context's user_data. In v4.3.0 the callback was not disarmed afterwards, so a second interface-down event forwarded the previously stored errno to zsock_accepted_cb(), which dereferenced it as the parent context and performed several stores through it (sock_set_error()'s read-modify-write of socket_data, k_fifo_cancel_wait(&parent->recv_q)) — the crash described in the fix's commit message. v4.3.1 and v4.4.x carry a later change clearing conn->accept_cb after the error callback (269cb8823d3 on the v4.3 branch, 913fae5169425550f2364655298fceb79b320066 on main), which closes that repeat path; on those releases the poisoned cookie remains reachable only by a narrower race, a handshake completing alongside the interface-down still passing the stale cookie to k_fifo_put(&parent->accept_q, ...), and by getsockopt(SO_ERROR), which reads the field back unconditionally. On v4.3.0 an application that keeps a listening TCP socket open across repeated link-down events is sufficient to reach the defect; the triggering condition is a network-interface state change, not attacker-supplied packet data, so the practical attacker is one able to force the link down repeatedly (for example an adjacent attacker disrupting a wireless link) or one with local/physical access. Because both the faulting address and the stored data are fixed small constants derived from the errno value, the outcome is a wild-pointer access leading to a kernel fatal error — a denial of service (device crash or reset) rather than an attacker-directed memory corruption. The fix stores the pending error in a dedicated net_context.sock_error field and converts every producer and consumer to sock_set_error()/sock_get_error(), leaving user_data untouched. As a side effect it also stops getsockopt(SO_ERROR) — which is evaluated unconditionally — from returning the kernel address held in user_data to a userspace application.

Metrics

CVSS 3.1

6.5/10

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Weakness Enumeration

CWE-843

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
zephyrproject	zephyr	>= 4.3.0, < 4.4.2

References

Timeline

Published: Sep 29, 2026
Last Modified: Sep 29, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-18417?

The native BSD-socket layer recorded a pending asynchronous socket error by type-punning it into struct net_context's void user_data field (ctx->user_data = INT_TO_POINTER(-status) in zsock_accepted_cb(), zsock_received_cb(), zsock_connected_cb() and zsock_close_ctx() in subsys/net/lib/sockets/sockets_inet.c), reading it back with POINTER_TO_INT(). That same field is owned by the network stack for listening TCP contexts: net_tcp_accept() stores the parent context pointer there and the TCP core passes it back to the registered accept callback. A failed accept therefore left a small integer (an errno value) where the stack expected a struct net_context . When the network interface carrying a listening TCP socket goes down, close_tcp_conn() in subsys/net/ip/tcp.c invokes the accept callback with -ENETDOWN and the context's user_data. In v4.3.0 the callback was not disarmed afterwards, so a second interface-down event forwarded the previously stored errno to zsock_accepted_cb(), which dereferenced it as the parent context and performed several stores through it (sock_set_error()'s read-modify-write of socket_data, k_fifo_cancel_wait(&parent->recv_q)) — the crash described in the fix's commit message. v4.3.1 and v4.4.x carry a later change clearing conn->accept_cb after the error callback (269cb8823d3 on the v4.3 branch, 913fae5169425550f2364655298fceb79b320066 on main), which closes that repeat path; on those releases the poisoned cookie remains reachable only by a narrower race, a handshake completing alongside the interface-down still passing the stale cookie to k_fifo_put(&parent->accept_q, ...), and by getsockopt(SO_ERROR), which reads the field back unconditionally. On v4.3.0 an application that keeps a listening TCP socket open across repeated link-down events is sufficient to reach the defect; the triggering condition is a network-interface state change, not attacker-supplied packet data, so the practical attacker is one able to force the link down repeatedly (for example an adjacent attacker disrupting a wireless link) or one with local/physical access. Because both the faulting address and the stored data are fixed small constants derived from the errno value, the outcome is a wild-pointer access leading to a kernel fatal error — a denial of service (device crash or reset) rather than an attacker-directed memory corruption. The fix stores the pending error in a dedicated net_context.sock_error field and converts every producer and consumer to sock_set_error()/sock_get_error(), leaving user_data untouched. As a side effect it also stops getsockopt(SO_ERROR) — which is evaluated unconditionally — from returning the kernel address held in user_data to a userspace application.

How severe is CVE-2026-18417?

CVE-2026-18417 has a CVSS score of 6.5/10 (MEDIUM severity).

How do I fix CVE-2026-18417?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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