NanoMQ MQTT Broker 0.24.6 Subscription strchr null pointer dereference

Summaryinfo

A vulnerability marked as problematic has been reported in NanoMQ MQTT Broker 0.24.6. Affected by this issue is the function strchr of the component Subscription Handler. The manipulation leads to null pointer dereference. This vulnerability is documented as CVE-2025-68699. The attack can be initiated remotely. There is not any exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in NanoMQ MQTT Broker 0.24.6. It has been rated as problematic. This issue affects the function strchr of the component Subscription Handler. The manipulation with an unknown input leads to a null pointer dereference vulnerability. Using CWE to declare the problem leads to CWE-476. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. Impacted is availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2025-68699 since 12/23/2025. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. It demands that the victim is doing some kind of user interaction. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 0.24.6 or 0.24.7 eliminates this vulnerability. Applying the patch 89d68d678e7f841ae7baa45cba8d9bc7ddc9ef4b is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Vendor

• NanoMQ

Name

• MQTT Broker

Version

• 0.24.6

License

• open-source

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