---
title: "CVE-2026-87121: lwIP TCP/IP Stack - Remote Code Execution"
description: "lwIP TCP/IP Stack MQTT contains an out-of-bounds write vulnerability in the MQTT component, letting attackers gain full code execution on the device, exploit requires network access."
url: https://panop.io/threat-heartbeat/CVE-2026-87121/
---

# CVE-2026-87121 lwIP TCP/IP Stack - Remote Code Execution

lwIP TCP/IP Stack MQTT contains an out-of-bounds write vulnerability in the MQTT component, letting attackers gain full code execution on the device, exploit requires network access.

CVSS base score 9.8 /10

Critical

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.53% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-87121)

## Details

Type

Remote Code Execution

Impact

Remote Code Execution

CVSS vector

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

Published

22 September 2026

Updated

15 October 2026

Weakness

[CWE-787](https://cwe.mitre.org/data/definitions/787.html)

## Vendor fix

Update to the latest version of lwIP TCP/IP Stack.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-87121](https://nvd.nist.gov/vuln/detail/CVE-2026-87121)
- [https://github.com/cisagov/CSAF/blob/develop/csaf\_files/OT/white/2026/icsa-26-265-01.json](https://github.com/cisagov/CSAF/blob/develop/csaf_files/OT/white/2026/icsa-26-265-01.json)
- [https://savannah.nongnu.org/projects/lwip](https://savannah.nongnu.org/projects/lwip)
- [https://www.cisa.gov/news-events/ics-advisories/icsa-26-265-01](https://www.cisa.gov/news-events/ics-advisories/icsa-26-265-01)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

Panop answers these inside your environment, for this CVE and every other finding.

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