Description
The asynchronous SNTP client in Zephyr (subsys/net/lib/sntp/sntp.c, sntp_close_async) closed the UDP socket file descriptor directly from the calling thread immediately after detaching it from the network socket service, without synchronizing with the socket-service poll thread.

The socket service thread polls each socket via zvfs_poll, which (in zsock_poll_prepare_ctx) registers a k_poll_event pointing into the socket's net_context (&ctx->recv_q) and then blocks in k_poll without holding a reference or lock. net_context objects are allocated from a fixed pool (contexts[CONFIG_NET_MAX_CONTEXTS]) and reused after close.

When sntp_close_async is invoked from a different thread than the poll thread (in the in-tree consumer subsys/net/lib/config/init_clock_sntp.c, the SNTP timeout handler runs on the system workqueue while the socket service thread is blocked in poll on the same fd), the close frees and may reuse the net_context while the poll thread still has a poller node linked into the freed object, resulting in a use-after-free / object confusion of kernel poll structures.

The SNTP timeout path is the normal no-response failure mode, so a network peer or off-path attacker who drops or delays the SNTP/NTP response can drive the racing close repeatedly (and periodically with NET_CONFIG_SNTP_INIT_RESYNC). The most likely consequence is a crash of the networking thread (denial of service), with potential memory corruption when the freed context slot is reallocated.

The fix defers the close to the socket service thread itself via net_socket_service_close (NET_SOCKET_SERVICE_CLOSE_SOCKETS), so the same thread that polls performs the close, eliminating the race. Affected releases: v4.2.0 through v4.4.0.
Published: 2026-06-30
Score: 6.5 Medium
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

Impact

A race condition in Zephyr’s asynchronous SNTP client causes the UDP socket to be closed and the underlying context freed while another thread is still polling that socket. This use‑after‑free can make the polling thread crash and may corrupt memory if the same context slot is reallocated. The failure is triggered when a network response is dropped or delayed, a scenario that an off‑path attacker can engineer by interfering with the SNTP/NTP reply. The most immediate outcome is a denial of service through a crash of the networking thread, with the possibility of memory corruption if the freed context is reused during the race.

Affected Systems

The vulnerability affects Zephyr OS releases from 4.2.0 through 4.4.0. It impacts systems that enable the SNTP client and rely on asynchronous operation, such as embedded devices and IoT platforms running Zephyr. Vendors using 4.2.0–4.4.0 should review if the SNTP functionality is in use.

Risk and Exploitability

The CVSS score of 6.5 classifies this as a medium‑severity issue. No EPSS score is available, and the vulnerability is not listed in CISA’s KEV catalog. The attack vector is external, via network traffic manipulation that induces the SNTP timeout path. Exploitation does not require privileged code or local access; an attacker can trigger the race by dropping or delaying the SNTP response. Because the crash directly impacts the networking thread, affected devices would experience service disruption without requiring further compromise.

Generated by OpenCVE AI on June 30, 2026 at 17:50 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Upgrade Zephyr to a release newer than v4.4.0 where the close is deferred to the socket service thread
  • Ensure the SNTP client is enabled only if the device requires NTP synchronization
  • If upgrading is not possible, apply the source patch that defers the close to the socket service thread (e.g., merge commit ef47bdf3), or implement a safe close sequence.

Generated by OpenCVE AI on June 30, 2026 at 17:50 UTC.

Tracking

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Advisories

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History

Tue, 30 Jun 2026 20:45:00 +0000

Type Values Removed Values Added
First Time appeared Zephyrproject
Zephyrproject zephyr
Vendors & Products Zephyrproject
Zephyrproject zephyr

Tue, 30 Jun 2026 18:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Tue, 30 Jun 2026 16:45:00 +0000

Type Values Removed Values Added
Description The asynchronous SNTP client in Zephyr (subsys/net/lib/sntp/sntp.c, sntp_close_async) closed the UDP socket file descriptor directly from the calling thread immediately after detaching it from the network socket service, without synchronizing with the socket-service poll thread. The socket service thread polls each socket via zvfs_poll, which (in zsock_poll_prepare_ctx) registers a k_poll_event pointing into the socket's net_context (&ctx->recv_q) and then blocks in k_poll without holding a reference or lock. net_context objects are allocated from a fixed pool (contexts[CONFIG_NET_MAX_CONTEXTS]) and reused after close. When sntp_close_async is invoked from a different thread than the poll thread (in the in-tree consumer subsys/net/lib/config/init_clock_sntp.c, the SNTP timeout handler runs on the system workqueue while the socket service thread is blocked in poll on the same fd), the close frees and may reuse the net_context while the poll thread still has a poller node linked into the freed object, resulting in a use-after-free / object confusion of kernel poll structures. The SNTP timeout path is the normal no-response failure mode, so a network peer or off-path attacker who drops or delays the SNTP/NTP response can drive the racing close repeatedly (and periodically with NET_CONFIG_SNTP_INIT_RESYNC). The most likely consequence is a crash of the networking thread (denial of service), with potential memory corruption when the freed context slot is reallocated. The fix defers the close to the socket service thread itself via net_socket_service_close (NET_SOCKET_SERVICE_CLOSE_SOCKETS), so the same thread that polls performs the close, eliminating the race. Affected releases: v4.2.0 through v4.4.0.
Title Use-after-free race in SNTP async client when closing the socket while the socket service is still polling it
Weaknesses CWE-416
References
Metrics cvssV3_1

{'score': 6.5, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H'}

Subscriptions

Zephyrproject Zephyr
cve-icon MITRE

Status: PUBLISHED

Assigner: zephyr

Published:

Updated: 2026-07-14T18:38:40.121Z

Reserved: 2026-06-02T15:24:29.575Z

Link: CVE-2026-10655

cve-icon Vulnrichment

Updated: 2026-06-30T16:41:47.172Z

cve-icon NVD

No data.

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-06-30T20:45:03Z

Weaknesses