A vulnerability exists in Mosquitto versions 0.15 to 1.4.11 inclusive known as CVE-2017-7650.
Pattern based ACLs can be bypassed by clients that set their username/client id to '#' or '+'. This allows locally or remotely connected clients to access MQTT topics that they do have the rights to. The same issue may be present in third party authentication/access control plugins for Mosquitto.
The vulnerability only comes into effect where pattern based ACLs are in use, or potentially where third party plugins are in use.
The issue is fixed in Mosquitto 1.4.12, which has just been released. Patches for older versions are available at https://mosquitto.org/files/cve/2017-7650
The fix addresses the problem by restricting access for clients with a '#', '+', or '/' in their username or client id. '/' has been included in the list of characters disallowed because it also has a special meaning in a topic and may represent an additional risk. The restriction placed on clients is that they may not receive or send messages that are subject to a pattern based ACL check, nor any message that is subject to a plugin check.
Thanks to Artem Zinenko from HackerDom CTF team for finding this vulnerability and responsibly reporting it.
Complete list of fixes addressed in version 1.4.12:
- Fix mosquitto.db from becoming corrupted due to client messages being persisted with no stored message. Closes #424.
- Fix bridge not restarting properly. Closes #428.
- Fix unitialized memory in
gets_quieton Windows. Closes #426.
- Fix building with
WITH_ADNS=nofor systems that don't use glibc. Closes #415.
- Fixes to readme.md.
- Fix deprecation warning for OpenSSL 1.1. PR #416.
- Don't segfault on duplicate bridge names. Closes #446.
- Fix CVE-2017-7650.