---
id: CVE-2026-87121
title: "lwIP\_TCP/IP Stack MQTT\_is vulnerable to an out-of-bounds write, which may allow an attacker to gain full code execution on the device."
summary: "lwIP\_TCP/IP Stack MQTT\_is vulnerable to an out-of-bounds write, which may allow an attacker to gain full code execution on the device."
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-787
vendor: lwIP
product: TCP/IP Stack MQTT
affected:
  - tcp_ip_stack_mqtt >= 2.0.1 <= 2.2.1
published: '2026-09-22'
updated: '2026-09-23'
sourceUpdated: '2026-09-23T19:42:48.540'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-87121'
references:
  - url: >-
      https://github.com/cisagov/CSAF/blob/develop/csaf_files/OT/white/2026/icsa-26-265-01.json
    label: ics-cert@hq.dhs.gov
  - url: 'https://savannah.nongnu.org/projects/lwip'
    label: ics-cert@hq.dhs.gov
  - url: 'https://www.cisa.gov/news-events/ics-advisories/icsa-26-265-01'
    label: ics-cert@hq.dhs.gov
tags:
  - nvd
  - cve.org
epss: 0.00528
epssPercentile: 0.42186
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: total
  timestamp: '2026-09-22T20:23:00.531481Z'
ingestedAt: '2026-09-22T20:10:15.095Z'
---

## Overview

lwIP TCP/IP Stack MQTT is vulnerable to an out-of-bounds write, which may allow an attacker to gain full code execution on the device.

## Remediation

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