-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

Advisory ID:               SYSS-2023-022 
Product:                   Zepp app, Amazfit Bip U
Manufacturer:              Huami Technology
Affected Version(s):       Zepp app 7.8.2 on Android 9, 10, 11; 
                           Amazfit Bip U v1.0.7.32
Tested Version(s):         Zepp app 7.8.2 on Android 9, 10, 11; 
                           Amazfit Bip U v1.0.7.32
Vulnerability Type:        Missing Encryption of Sensitive Data (CWE-311)
Risk Level:                Medium
Solution Status:           Open
Manufacturer Notification: 2023-08-18
Solution Date:             N/A
Public Disclosure:         2023-10-09
CVE Reference:             N/A
Authors of Advisory:       Julia Karel, Tobias Jäger, SySS GmbH

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Overview:

The Amazfit Bip U (see [1]) is a smartwatch with health functions. The Zepp app
on Android (see [2]) is an app which is used to connect the watch to the
smartphone and which handles the communication.

Due to missing pairing of the Bluetooth Low Energy connection, it remains
unencrypted. Therefore, all data transferred between the smartphone and the
smartwatch can be eavesdropped. This only concerns the Android version of the
app.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Vulnerability Details:

When connecting an Amazfit Bip U smartwatch to the Zepp app on an Android
device, the connection is established using Bluetooth Low Energy (BLE). In the
BLE standard, pairing is used to negotiate a key which is used to establish an
encrypted connection. Bonding is then used to store a long-term key on both
devices, so they can establish encrypted connections without performing a 
pairing again. 

The Zepp app on Android is not initiating a pairing and bonding with the
smartwatch. Therefore, no encryption key is negotiated and the traffic between
the Amazfit Bip U and the Android smartphone remains unencrypted. There is also
no self-managed encryption implemented. Thus, all health data and all
messages that are transferred to and from the smartwatch can be eavesdropped if
the attacker is within the BLE range of the devices. 

If the Zepp app is used on iOS, the pairing and bonding is performed and the
connection is therefore encrypted.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Proof of Concept (PoC):

By sniffing the Bluetooth Low Energy connection between the Amazfit Bip U and
the Android 11 smartphone with the Zepp app installed, messages of different
messengers could be eavesdropped.

The developed tool AmazfitSniffer, which is based on the tool Sniffle (see [5]),
is then eavesdropping and parsing messages of different messengers. 

> python3 ./amazfitSniffer.py -m [MAC address of Amazfit Bip U] 

Connection to the smartwatch found and eavesdropping...

Telegram message intercepted: 
 Sender: John Doe
 Message: Very secret message
WhatsApp message intercepted: 
 Sender: Max Mustermann
 Message: Did you know, that John Doe...

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Solution:

- -

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Disclosure Timeline:

2021-09-28: Vulnerability discovered
2023-08-18: Vulnerability reported to manufacturer
N/A: Patch released by manufacturer
2023-10-09: Public disclosure of vulnerability

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

References:

[1] Product website for the Amazfit Bip U
    https://de.amazfit.com/products/amazfit-bip-u
[2] Google Play Store website for the Zepp app
    https://play.google.com/store/apps/details?id=com.huami.watch.hmwatchmanager&hl=de&gl=US
[3] SySS Security Advisory SYSS-2023-022
    https://www.syss.de/fileadmin/dokumente/Publikationen/Advisories/SYSS-2023-022.txt
[4] SySS Responsible Disclosure Policy
    https://www.syss.de/en/responsible-disclosure-policy
[5] Bluetooth Low Energy sniffer Sniffle
    https://github.com/nccgroup/Sniffle

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Credits:

This security vulnerability was found by Julia Karel and published and verified
by Tobias Jäger of SySS GmbH.

E-Mail: tobias.jaeger@syss.de
Public Key: https://www.syss.de/fileadmin/dokumente/PGPKeys/Tobias_Jaeger.asc
Key ID: 0xABF0CF2F4D0220F9
Key Fingerprint: 5C9F 5312 F37E B9AB E87B 1212 ABF0 CF2F 4D02 20F9

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Copyright:

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

-----BEGIN PGP SIGNATURE-----
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=b86d
-----END PGP SIGNATURE-----