XSS in error pages


 * 1) REDIRECT Cross-site Scripting (XSS)

Description
While creating dynamiac web pages it's easy to make a mistake. If a generated page depends on entered data (e.g. URI, HTTP headers etc.) and these data are not filtered enough, it is possible that it can be exploited using XSS technique.

Risk Factors
TBD

Examples
Example 1

Let's assume that we have an error page, which is handling requests for a non existing pages. Classic 404 error page. We may use the code below as an example to inform user about what specific page is missing:

<? php print "Not found: ". urldecode($_SERVER["REQUEST_URI"]); ?>

Let's see how does it work: http://testsite.test/file_which_not_exist In response we got: Not found: /file_which_not_exist Now we will try to force the error page to include our code: http://testsite.test/ alert("TEST"); The result is: Not found: / (but with JavaScript code alert("TEST"); ) We have successfully injected the code, our XSS! What does it mean? E.g. that we may try to steal the cookies. Problems which may occur using XSS techique are:
 * escaping data entered by the user (e.g. character " after escaping will be \"),
 * maximum length of the URI, which HTTP server will accept.

Related Threat Agents

 * TBD

Related Attacks

 * XSS Attacks
 * Category:Injection Attack
 * Invoking untrusted mobile code

Related Vulnerabilities

 * Category:Input Validation Vulnerability

Related Controls

 * Category:Input Validation Control
 * HTML Entity Encoding