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.
CVE-2026-87121
CRITICALPre-NVD 9.89.8—
EchelonGraph scoreHIGH confidence
Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2026-09-22. a secondary CVSS source baseline 9.8; sources differ by 0.0.
Triggered by: GitHub Security Advisory CVSS
Sources: ghsa, secondary
9.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
- High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: —CVSS: 9.8Exploit: None knownExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 9.8
- EG Score
- 9.8(high)
- EG Risk
- 49(Track)EG Risk 49/100SSVC: Track
EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).
How it’s computedSeverity98% × 45%Exploitation0% × 40%Automatability30% × 15%Action: Routine — remediate on your standard cadence. - EPSS PROB
- —
- EPSS %ILE
- —
- KEV
- Not listed
Published
September 22, 2026
Last Modified
September 22, 2026
References (3)
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Frequently asked(4)
What is CVE-2026-87121?
CVE-2026-87121 is a critical vulnerability published on September 22, 2026. 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.
When was CVE-2026-87121 disclosed?
CVE-2026-87121 was first published in the National Vulnerability Database on September 22, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
What is the CVSS score of CVE-2026-87121?
CVE-2026-87121 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2026-87121?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-87121, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.
Dependency Blast Radius
Explore the affected products and dependency analysis for CVE-2026-87121
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