Vulnerability · Published Sep 22, 2026 · Assigned by icscert
CVE-2026-87121Out-of-bounds write in lwIP TCP/IP Stack MQTT Client Application
Critical 9.8
In plain English
A critical-severity out-of-bounds write in TCP/IP Stack MQTT from lwIP. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.8% (higher than 56% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)9.8Critical
Exploit odds (30 days)0.8%top 44.0% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | lwip | no fix listed | DEBIAN-CVE-2026-87121 |
| Debian:13 | lwip | no fix listed | DEBIAN-CVE-2026-87121 |
| Debian:14 | lwip | 2.2.1+dfsg1-8 | DEBIAN-CVE-2026-87121 |
| Ubuntu:26.10 | lwip | no fix listed | UBUNTU-CVE-2026-87121 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| lwIP | TCP/IP Stack MQTT | 2.0.1 – through 2.2.1 |
Weakness: CWE-787 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H