What is CVE-2026-87121?

CVE-2026-87121 is a critical-severity vulnerability in Lwip Tcp/ip Stack Mqtt, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2026-09-22.

How severe is CVE-2026-87121?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Buffer overflow in Lwip Tcp/ip Stack Mqtt

CVE-2026-87121

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.

Vulnerability class: Buffer Overflow

Published 2026-09-22 · last modified 2026-09-22.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Lwip Tcp/ip Stack Mqtt

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

References

savannah.nongnu.org/projects/lwip
www.cisa.gov/news-events/ics-advisories/icsa-26-265-01
github.com/cisagov/CSAF/blob/develop/csaf_files/OT/white/2026/icsa-26-265-01.js…

Frequently asked questions

What is CVE-2026-87121?: CVE-2026-87121 is a critical-severity vulnerability in Lwip Tcp/ip Stack Mqtt, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2026-09-22.
How severe is CVE-2026-87121?: Critical severity. CVSS v3 base score is 9.8 out of 10.