# CVE-2026-73863: NanoMQ heap buffer over-read in MQTT SUBSCRIBE parsing

Source: https://junglewise.ai/threats/cve-2026-73863-nanomq-is-an-mqtt-broker-prior-to-0-24-14-nanomq-s-broker-side  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-18. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-73863 · Severity: info · Published 2026-09-18

NanoMQ is an open-source MQTT message broker used for IoT and real-time messaging. A remote attacker can crash the broker by sending a malformed MQTT SUBSCRIBE packet, causing a denial of service. The vulnerability affects the broker's message parsing logic and allows an unauthenticated client to trigger a heap buffer over-read without requiring any special network conditions.

Vendors: [NanoMQ](https://junglewise.ai/threats/vendors/nanomq).

## Quick answers

**Is CVE-2026-73863 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-73863 being exploited in the wild.

**How severe is CVE-2026-73863?** Informational severity, published 18 September 2026.

**Which products and versions are affected?** NanoMQ prior to 0.24.14.

**Is there a fix for CVE-2026-73863?** A patch was published on 2026-05-20: Fix merged in PR #1518 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-73863 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-73863?** Check whether you run NanoMQ at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The nmq_subinfo_decode() function in mqtt_parser.c incorrectly reuses the outer Properties Length variable when parsing multiple SUBSCRIPTION_IDENTIFIER fields, causing get_var_integer() to read from an incorrect heap offset. An attacker sends a SUBSCRIBE packet with a multi-byte Properties Length and repeated subscription identifiers to trigger the over-read. The flaw is remotely exploitable and results in broker crash; a patch is available in version 0.24.14.

## Affected products

- NanoMQ NanoMQ prior to 0.24.14

## Timeline

- 2026-09-18: disclosed
- 2026-05-20: patched: Fix merged in PR #1518

## References

- [https://github.com/nanomq/NanoNNG/commit/f888fe39d6691b253ff9aee598ce58bbe449ab6f](https://github.com/nanomq/NanoNNG/commit/f888fe39d6691b253ff9aee598ce58bbe449ab6f)
- [https://github.com/nanomq/NanoNNG/pull/1518](https://github.com/nanomq/NanoNNG/pull/1518)