# CVE-2026-44639: NanoMQ: O(N²) Denial of Service in MQTT v5 Property Parsing

> Remote unauthenticated attackers can cause denial of service in NanoMQ by sending packets with many User Properties, triggering excessive CPU usage.

- **Severity:** Low 3.7 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 18 Sep 2026
- **Updated:** 18 Sep 2026
- **Also known as:** GHSA-6mwg-445v-2qrv

## What is CVE-2026-44639?

CVE-2026-44639 is a low-severity denial of service vulnerability in nanomq, published on 18 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

NanoMQ is an MQTT broker. Prior to 0.24.14, NanoMQ's MQTT v5 property decoder in nng/src/supplemental/mqtt/mqtt_codec.c uses property_append() to walk the entire linked list for each property added by decode_buf_properties(). A remote unauthenticated client can supply a PUBLISH or SUBSCRIBE packet containing many User Properties, causing O(N²) linked-list insertion and CPU work that makes the broker unresponsive; repeated packets can sustain the denial of service. This issue is fixed in version 0.24.14.

Weakness: CWE-407 (Inefficient Algorithmic Complexity)

## Which versions are affected by CVE-2026-44639?


## How do I fix CVE-2026-44639?

No fix has been published for CVE-2026-44639 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-44639 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44639 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-44639 and fix it if it is affected.

What it is: CVE-2026-44639 is a low-severity denial of service vulnerability in nanomq, published on 18 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-44639 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-2026-44639/ (Markdown: https://insights.sbomify.com/CVE-2026-44639/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-44639
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-44639
- OSV: https://osv.dev/vulnerability/CVE-2026-44639

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-44639/
Summaries are generated and may contain mistakes; the official description above is the record.