Out-of-bounds write in lwIP TCP/IP Stack MQTT Client Application (CVE-2026-87121) | HOL Guard CVE

Critical · CVSS 9.3CVE-2026-87121

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

Answer in brief

CVE-2026-87121 records a Critical severity (CVSS 9.3) vulnerability in Out-of-bounds write in lwIP TCP/IP Stack MQTT Client Application. The current sources do not mark it as known exploited. The current feed maps lwIP/TCP/IP Stack MQTT (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 22, 2026Updated Sep 22, 2026Source checked Sep 22, 2026First seen by HOL Sep 22, 2026Material review Sep 22, 2026

Upstream Advisory

Key facts

Risk: Critical · CVSS 9.3
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Not reported

Why this deserves its current priority

CVSS is 9.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps lwIP/TCP/IP Stack MQTT (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
lwIP/TCP/IP Stack MQTTgeneric	>=2.0.1 <=2.2.1	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for lwIP/TCP/IP Stack MQTT.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
Sep 22, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 22, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 22, 2026

Sources and claim methodology

Upstream source description

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.

Quoted source text, attributed separately from HOL analysis.