# CVE-2026-47275: nanomq NULL Pointer Dereference in MQTTv5 Client CONNECT Decoder Leading to Remote DoS

> A malicious MQTT broker can crash NanoMQ clients via a NULL pointer dereference in the CONNECT decoder, causing remote denial of service.

- **Severity:** Low 2.6 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 20 Jul 2026
- **Updated:** 20 Jul 2026
- **Also known as:** GHSA-52qr-3v49-wmx6

## What is CVE-2026-47275?

CVE-2026-47275 is a low-severity vulnerability in nanomq, published on 20 Jul 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

In nanomq versions 0.24.11 and earlier, a NULL pointer dereference in `nni_mqttv5_msg_decode_connect()` allows a malicious MQTT broker to crash any connecting NanoMQ MQTTv5 client (including bridge mode) with a single packet, causing remote denial of service via SIGSEGV. In `nni_mqttv5_msg_decode_connect()` (`mqtt_codec.c:1863`), the code iterates over CONNECT properties using variable `prop` when it should use `will_prop`. When a CONNECT packet has no connect-level properties (`prop == NULL`) but has will properties (`will_prop != NULL`), dereferencing `prop->next` causes SIGSEGV at address `0x38` (NULL + `offsetof(property, next)`).

This affects both `nanomq_cli` and **NanoMQ bridge mode** (Core component), as both use the same `mqtt_client.c` receive path. This can lead to remote DoS if a malicious MQTT broker can crash the client process with a single 35-byte packet and persistent DoS if auto-reconnect causes infinite crash loop.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2026-47275?


## How do I fix CVE-2026-47275?

No fix has been published for CVE-2026-47275 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-47275 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-47275 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-47275 and fix it if it is affected.

What it is: CVE-2026-47275 is a low-severity vulnerability in nanomq, published on 20 Jul 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-47275 exists.

Affected product: nanomq. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-47275/ (Markdown: https://insights.sbomify.com/CVE-2026-47275/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-47275
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-47275
- OSV: https://osv.dev/vulnerability/CVE-2026-47275

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-47275/
Summaries are generated and may contain mistakes; the official description above is the record.