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 · last modified .

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

EPSS: 0.008 (55.8th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 56th percentile — 55.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-87121: held from 0.005 to 0.008.

EPSS over last 30 days · oldest: 0.005 · newest: 0.008 · change: +0.002

Affected products

Weakness classification (CWE)

References

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.