CVE-2026-87121 Out-of-bounds write in lwIP TCP/IP Stack MQTT Client Application
An out-of-bounds write in the lwIP MQTT client allows attackers to achieve full code execution on affected devices.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-87121?
CVE-2026-87121 is a critical memory corruption vulnerability in lwIP TCP/IP Stack MQTT, published on 22 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-787
Which versions are affected by CVE-2026-87121?
How do I fix CVE-2026-87121?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-87121 being exploited?
There is no known exploitation of CVE-2026-87121 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-87121, GHSA-h8q6-7rjx-3m2r, UBUNTU-CVE-2026-87121.