//=====================>> Security Advisory <<=====================// --------------------------------------------------------------------- XSS vulnerabilities in Google.com --------------------------------------------------------------------- --[ Author: Yair Amit , Watchfire Corporation http://www.watchfire.com --[ Discovery Date: 15/11/2005 --[ Initial Vendor Response: 15/11/2005 --[ Issue solved: 01/12/2005 --[ Website: www.google.com --[ Severity: High --[ Summary Two XSS vulnerabilities were identified in the Google.com website, which allow an attacker to impersonate legitimate members of Google's services or to mount a phishing attack. Although Google uses common XSS countermeasures, a successful attack is possible, when using UTF-7 encoded payloads. --[ Background Google's URL redirection script --------------------------------------------------------------------- The script (http://www.google.com/url?q=...) is normally used for redirecting the browser from Google's website to other sites. For example, the following request will redirect the browser to http://www.watchfire.com : - http://www.google.com/url?q=http://www.watchfire.com When the parameter (q) is passed to the script with illegal format (The format seems to be: http://domain), a "403 Forbidden" page returns to the user, informing that the query was illegal. The parameter's value appears in the html returned to the user. If http://www.google.com/url?q=USER_INPUT is requested, the text in the "403 Forbidden" response would be: - "Your client does not have permission to get URL /url?q=USER_INPUT from this server." The server response lacks charset encoding enforcement, such as: * Response headers: "Content-Type: text/html; charset=[encoding]". * Response body: "<meta http-equiv="Content-Type" (...) charset=[encoding]/>". Google's 404 NOT FOUND mechanism --------------------------------------------------------------------- When requesting a page which doesn't exist under www.google.com, a 404 NOT FOUND response is returned to the user, with the original path requested. If http://www.google.com/NOTFOUND is requested, the following text appears in the response: "Not Found The requested URL /NOTFOUND was not found on this server." The server response lacks charset encoding enforcement, such as: * Response headers: "Content-Type: text/html; charset=[encoding]". * Response body: "<meta http-equiv="Content-Type" (...) charset=[encoding]/>". --[ XSS vulnerabilities While the aforementioned mechanisms (URL redirection script, 404 NOT FOUND) escape common characters used for XSS, such as <> (triangular parenthesis) and apostrophes, it fails to handle hazardous UTF-7 encoded payloads. Therefore, when sending an XSS attack payload, encoded in UTF-7, the payload will return in the response without being altered. For the attack to succeed (script execution), the victim's browser should treat the XSS payload as UTF-7. --[ IE charset encoding Auto-Selection If 'Encoding' is set to 'Auto-Select', and Internet-Explorer finds a UTF-7 string in the first 4096 characters of the response's body, it will set the charset encoding to UTF-7 automatically, unless a certain charset encoding is already enforced. This automatic encoding selection feature makes it possible to mount UTF-7 XSS attacks on Google.com. --[ Solution Google solved the aforementioned issues at 01/12/2005, by using character encoding enforcement. --[ Acknowledgement The author would like to commend the Google Security Team for their cooperation and communication regarding this vulnerability.
This archive was generated by hypermail 2.1.3 : Wed Dec 21 2005 - 12:14:56 PST