boneIO black_debian_images stores the Mosquitto MQTT broker password file at /etc/mosquitto/passwd with world-readable permissions. Any local user can read the password hashes for all MQTT accounts and perform offline dictionary attacks.
This issue was fixed in version 1.6.0.
Incorrect Permission Assignment for Critical Resource The product specifies permissions for a security-critical resource in a way that allows that resource to be read or modified by unintended actors.