CVE-2026-25627 nanomq: OOB Read / Crash (DoS) via Malformed MQTT Remaining Length over WebSocket
Remote attackers can crash the NanoMQ MQTT broker by sending malformed WebSocket packets with large remaining lengths, causing an out-of-bounds read.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-25627?
CVE-2026-25627 is a medium-severity denial of service vulnerability in nanomq, published on 30 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
NanoMQ MQTT Broker (NanoMQ) is an all-around Edge Messaging Platform. Prior to version 0.24.8, NanoMQ’s MQTT-over-WebSocket transport can be crashed by sending an MQTT packet with a deliberately large Remaining Length in the fixed header while providing a much shorter actual payload. The code path copies Remaining Length bytes without verifying that the current receive buffer contains that many bytes, resulting in an out-of-bounds read (ASAN reports OOB / crash). This is remotely triggerable over the WebSocket listener. This issue has been patched in version 0.24.8.
Weakness: CWE-125
Which versions are affected by CVE-2026-25627?
It affects 1 product.
Products include Emqx Nanomq.
How do I fix CVE-2026-25627?
No fix has been published for CVE-2026-25627 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-25627 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-25627 exists.
Other vulnerabilities in nanomq
Sources
Also known as GHSA-w4rh-v3h2-j29x.