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Advisory ID:               SYSS-2023-013 
Product:                   Miniserver Go Gen.2
Manufacturer:              Loxone
Affected Version(s):       <14.0.3.28
Tested Version(s):         14.0.3.28, 13.1.11.17
Vulnerability Type:        Use of Hard-coded Cryptographic Key (CWE-321)
Risk Level:                Low
Solution Status:           Fixed
Manufacturer Notification: 2023-05-03
Solution Date:             2023-06-20
Public Disclosure:         2023-06-30
CVE Reference:             CVE-2023-36623
Author of Advisory:        Tobias Jäger, SySS GmbH
                           Moritz Abrell, SySS GmbH

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Overview:

The Loxone Miniserver Go is a smart home hub.

The manufacturer describes the product as follows (see [1]):

"The Loxone Miniserver Go serves as central control unit for all kinds 
of automation tasks."

Due to the use of hardcoded keys, the root password can be derived from
the MAC address.

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Vulnerability Details:

The Loxone Miniserver is calculating the root password using the command
"miniserverinit setpwd". The root password is derived from the MAC
address of the Miniserver, using hardcoded cryptographic keys.

The root password is calculated by encrypting the MAC address of the
device using the AES256-CBC algorithm. The encryption key and
initialization vector are hardcoded in the binary "miniserverinit". 

The ciphertext is then Base64-encoded and, additionally, some characters
are substituted. The root password is then the 20 character long 
substring, starting with the 10th character.

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Proof of Concept (PoC):

# python3 calc_root_pw.py 50:4f:94:a5:b1:e4
Root password: VRuM10yZrBRMuC1gi7qy

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Solution:

Install firmware version 14.2.

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Disclosure Timeline:

2023-04-21: Vulnerability discovered
2023-05-03: Vulnerability reported to manufacturer
2023-06-20: Patch released by manufacturer
2023-06-30: Public disclosure of vulnerability

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References:

[1] Product website for the Loxone Miniserver Go
    https://www.loxone.com/dede/kb/miniserver-go/
[2] SySS Security Advisory SYSS-2023-013
    https://www.syss.de/fileadmin/dokumente/Publikationen/Advisories/SYSS-2023-013.txt
[3] SySS Responsible Disclosure Policy
    https://www.syss.de/en/responsible-disclosure-policy

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Credits:

This security vulnerability was found by Tobias Jäger and Moritz Abrell of SySS GmbH.

E-Mail: tobias.jaeger@syss.de
Public Key: https://www.syss.de/fileadmin/dokumente/PGPKeys/Tobias_Jaeger.asc
Key Fingerprint: 5C9F 5312 F37E B9AB E87B 1212 ABF0 CF2F 4D02 20F9

E-Mail: moritz.abrell@syss.de
Public Key: https://www.syss.de/fileadmin/dokumente/PGPKeys/Moritz_Abrell.asc
Key Fingerprint: 2927 7EB6 1A20 0679 79E9  87E6 AE0C 9BF8 F134 8B53

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Disclaimer:

The information provided in this security advisory is provided "as is" 
and without warranty of any kind. Details of this security advisory may
be updated in order to provide as accurate information as possible. The
latest version of this security advisory is available on the SySS website.

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Copyright:

Creative Commons - Attribution (by) - Version 3.0
URL: http://creativecommons.org/licenses/by/3.0/deed.en

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