Out-of-bounds write in lwIP TCP/IP Stack MQTT Client Application

published 2026-09-22 47 d ago modified 2026-09-23 46 d ago also EUVD-2026-84816

cvss: 9.8; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.8%; EPSS 0.8% chance of exploitation in 30 days, percentile 56%
public exploits: 0; none known

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.

Patch / fix

distros 1

lwip Debian 14 2.2.1+dfsg1-8

debian advisories DEBIAN-CVE-2026-87121

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-87121 updated 2026-10-09 cvss 9.8

lwip: lwip: Arbitrary code execution via MQTT out-of-bounds write

Red Hat All currently supported Red Hat products
not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

cisa ICSA-26-265-01 updated 2026-09-22 cvss 9.8

lwIP TCP/IP Stack MQTT Client Application

lwIP MQTT Client Application >=2.0.1, <=2.2.1
affected: mitigation savannah.nongnu.org

From CISA ICS and IT advisories (CSAF, https://github.com/cisagov/CSAF), a U.S. Government work; changed: reduced to products, statuses and remediations. CISA notification · csaf

CISA SSVC

Exploitation: none
Automatable: yes
Technical impact: total
Assessed: 47 d ago (2026-09-22)

Exploit prediction

0.78% chance of exploitation in the next 30 days, higher than 56% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	9.8	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA	4.0	9.3	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CNA	4.0	9.3	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected products

lwIP TCP/IP Stack MQTT

Classification

Weakness

CWE-787 Out-of-bounds Write

References

Sources

CVE List CVE-2026-87121
NVD CVE-2026-87121

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary