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

> A remote attacker can crash the NanoMQ MQTT broker by sending a malformed shared subscription topic, causing a null pointer dereference.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 4 Feb 2026
- **Updated:** 4 Feb 2026
- **Also known as:** GHSA-qv5f-c6v2-2f8h

## What is CVE-2025-68699?

CVE-2025-68699 is a medium-severity vulnerability in nanomq, published on 4 Feb 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official 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.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2025-68699?

It affects 1 product.


Products: Emqx Nanomq.

## How do I fix CVE-2025-68699?

No fix has been published for CVE-2025-68699 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-68699 being exploited?

There is no known exploitation of CVE-2025-68699 in the wild and no public exploit code.

## Other vulnerabilities in nanomq

- [CVE-2024-42655](https://insights.sbomify.com/CVE-2024-42655/): Missing authorization in n/a (high 8.8)
- [CVE-2025-59947](https://insights.sbomify.com/CVE-2025-59947/): NanoMQ has Buffer Overflow (high 8.5)
- [CVE-2023-34488](https://insights.sbomify.com/CVE-2023-34488/): Memory corruption in n/a (high 8.0)
- [CVE-2026-32135](https://insights.sbomify.com/CVE-2026-32135/): NanoMQ has Heap Buffer Overflow in URI Parameter Parsing (high 7.7)
- [CVE-2026-36590](https://insights.sbomify.com/CVE-2026-36590/): Denial of service in n/a (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-68699 and fix it if it is affected.

What it is: CVE-2025-68699 is a medium-severity vulnerability in nanomq, published on 4 Feb 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2025-68699 in the wild and no public exploit code.

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-2025-68699/ (Markdown: https://insights.sbomify.com/CVE-2025-68699/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-68699
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-68699
- OSV: https://osv.dev/vulnerability/CVE-2025-68699

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-68699/
Summaries are generated and may contain mistakes; the official description above is the record.