CVE-2026-21888 MQTT v5 Variable Byte Integer parsing out-of-bounds: get_var_integer()

High 7.5 Published 11 Mar 2026 Updated 11 Mar 2026

An out-of-bounds read in NanoMQ's MQTT v5 parser allows attackers to crash the broker via malformed variable byte integers.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: None listed

What is CVE-2026-21888?

CVE-2026-21888 is a high-severity memory corruption vulnerability in nanomq, published on 11 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

NanoMQ MQTT Broker (NanoMQ) is an all-around Edge Messaging Platform. MQTT v5 Variable Byte Integer parsing out-of-bounds: get_var_integer() accepts 5-byte varints without bounds checks; reliably triggers OOB read / crash when built with ASan. This affects 0.24.6 and earlier.

Weakness: CWE-125

Which versions are affected by CVE-2026-21888?

It affects 1 product.

Products include Emqx Nanomq.

How do I fix CVE-2026-21888?

No fix has been published for CVE-2026-21888 yet. Limit exposure of the affected software until one is available.

Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.

Is CVE-2026-21888 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-21888 exists.

Sources

Also known as GHSA-cggc-6m7w-j7x5.