---
id: CVE-2026-15891
title: >-
  The MQTT-SN client keepalive handler process_ping() in
  subsys/net/lib/mqtt_sn/mqtt_sn.c removes the gateway record after PINGREQ
  retries are exhausted
summary: >-
  The MQTT-SN client keepalive handler process_ping() in
  subsys/net/lib/mqtt_sn/mqtt_sn.c removes the gateway record after PINGREQ
  retries are exhausted. It invoked
  SYS_SLIST_PEEK_HEAD_CONTAINER(&client->gateways, gw, next) but discarded t…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-476
vendor: zephyrproject
product: zephyr
affected:
  - zephyr >= 4.1.0 < 4.4.2
published: '2026-09-13'
updated: '2026-09-14'
sourceUpdated: '2026-09-14T21:10:41.650'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-15891'
references:
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/commit/bd21e954c36be105a374bbc090623810f1a17ee3
    label: vulnerabilities@zephyrproject.org
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-c4g8-4f9p-4746
    label: vulnerabilities@zephyrproject.org
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-14T12:55:24.444356Z'
ingestedAt: '2026-09-14T15:23:07.429Z'
epss: 0.00336
epssPercentile: 0.24272
---

## Overview

The MQTT-SN client keepalive handler process_ping() in subsys/net/lib/mqtt_sn/mqtt_sn.c removes the gateway record after PINGREQ retries are exhausted. It invoked SYS_SLIST_PEEK_HEAD_CONTAINER(&client->gateways, gw, next) but discarded the result. That macro is a pure expression that does not assign to gw, so gw retained its NULL initializer regardless of the list contents.

The code then dereferences the NULL gw (gw->gw_id) and passes it to mqtt_sn_gw_destroy(), reaching k_mem_slab_free(&gateways, NULL). With CONFIG_MEM_SLAB_POINTER_VALIDATE enabled this triggers k_panic(); in the default configuration it performs a write through the NULL pointer ((char )mem = slab->free_list;) and corrupts the slab free list. The outcome is a crash/kernel panic or, on targets where address 0 is writable, silent memory-allocator corruption.

The vulnerable branch runs whenever the connected MQTT-SN gateway fails to answer keepalive PINGREQs for the configured number of retries. This condition is controlled by the remote peer: a malicious or compromised gateway, or an on-path/adjacent attacker that advertises itself as a gateway and then stops responding (or blackholes the real gateway's PINGRESPs), forces the client into the defect. MQTT-SN runs over UDP and no authentication is required.

The impact is a remotely triggerable denial of service (availability) of the affected MQTT-SN client; there is no attacker-controlled data written. The sibling remover process_advertise() uses SYS_SLIST_FOR_EACH_CONTAINER_SAFE and is not affected. The fix assigns the macro's return value to gw.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.