If left unpatched, CVE-2026-18417 could lead to major system disruptions or data loss.
Status: Received on 29 Sep 2026, 00:17 UTC
Published on: 29 Sep 2026, 00:17 UTC
CVSS Release: version 3
vulnerabilities@zephyrproject.org
Secondary
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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.
The exploitability of CVE-2026-18417 depends on two key factors: attack complexity (the level of effort required to execute an exploit) and privileges required (the access level an attacker needs).
With low attack complexity and no required privileges, CVE-2026-18417 is an easy target for cybercriminals. Organizations should prioritize immediate mitigation measures to prevent unauthorized access and data breaches.
A lower complexity and fewer privilege requirements make exploitation easier. Security teams should evaluate these aspects to determine the urgency of mitigation strategies, such as patch management and access control policies.
Attack Complexity (AC) measures the difficulty in executing an exploit. A high AC means that specific conditions must be met, making an attack more challenging, while a low AC means the vulnerability can be exploited with minimal effort.
Privileges Required (PR) determine the level of system access necessary for an attack. Vulnerabilities requiring no privileges are more accessible to attackers, whereas high privilege requirements limit exploitation to authorized users with elevated access.
Above is the CVSS Sub-score Breakdown for CVE-2026-18417, illustrating how Base, Impact, and Exploitability factors combine to form the overall severity rating. A higher sub-score typically indicates a more severe or easier-to-exploit vulnerability.
Below is the Impact Analysis for CVE-2026-18417, showing how Confidentiality, Integrity, and Availability might be affected if the vulnerability is exploited. Higher values usually signal greater potential damage.
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