What’s Vulnerable › Vulnerabilities

CVE-2026-87121: Out-of-bounds write in lwIP TCP/IP Stack MQTT Client Application

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.8% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-22 · updated 2026-09-23
• Weakness: CWE-787

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.

Affected products

• lwIP TCP/IP Stack MQTT: from 2.0.1 through 2.2.1

References

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

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