CVE-2025-68699 NanoMQ $share/ Subscription Validation and Forwarding Parsing Inconsistency: NULL Pointer Increment Causes Crash
A remote attacker can crash the NanoMQ MQTT broker by sending a malformed shared subscription topic, causing a null pointer dereference.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2025-68699?
CVE-2025-68699 is a medium-severity vulnerability in nanomq, published on 4 Feb 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
NanoMQ MQTT Broker (NanoMQ) is an all-around Edge Messaging Platform. In version 0.24.6, NanoMQ has a protocol parsing / forwarding inconsistency when handling shared subscriptions ($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
Which versions are affected by CVE-2025-68699?
It affects 1 product.
Products include 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
Sources
Also known as GHSA-qv5f-c6v2-2f8h.