Reflected XSS, Cross Site Scripting, CWE-79, CAPEC-86, DORK, GHDB,

CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Report generated by XSS.CX at Mon Apr 25 09:29:06 CDT 2011.


Hoyt LLC Research investigates and reports on security vulnerabilities embedded in Web Applications and Products used in wide-scale deployment.

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1. Cross-site scripting (reflected)

1. Cross-site scripting (reflected)


Severity:   High
Confidence:   Certain
Path:   /

Issue detail

The name of an arbitrarily supplied request parameter is copied into the value of an HTML tag attribute which is encapsulated in single quotation marks. The payload 6483e%2527style%253d%2527x%253aexpression%2528alert%25281%2529%2529%2527be136aaa48c was submitted in the name of an arbitrarily supplied request parameter. This input was echoed as 6483e'style='x:expression(alert(1))'be136aaa48c in the application's response.

This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response. The PoC attack demonstrated uses a dynamically evaluated expression with a style attribute to introduce arbirary JavaScript into the document. Note that this technique is specific to Internet Explorer, and may not work on other browsers.

The application attempts to block certain characters that are often used in XSS attacks but this can be circumvented by double URL-encoding the required characters - for example, by submitting %253c instead of the < character.

Note that a redirection occurred between the attack request and the response containing the echoed input. It is necessary to follow this redirection for the attack to succeed. When the attack is carried out via a browser, the redirection will be followed automatically.

Remediation detail

There is probably no need to perform a second URL-decode of the name of an arbitrarily supplied request parameter as the web server will have already carried out one decode. In any case, the application should perform its input validation after any custom canonicalisation has been carried out.

Issue background

Reflected cross-site scripting vulnerabilities arise when data is copied from a request and echoed into the application's immediate response in an unsafe way. An attacker can use the vulnerability to construct a request which, if issued by another application user, will cause JavaScript code supplied by the attacker to execute within the user's browser in the context of that user's session with the application.

The attacker-supplied code can perform a wide variety of actions, such as stealing the victim's session token or login credentials, performing arbitrary actions on the victim's behalf, and logging their keystrokes.

Users can be induced to issue the attacker's crafted request in various ways. For example, the attacker can send a victim a link containing a malicious URL in an email or instant message. They can submit the link to popular web sites that allow content authoring, for example in blog comments. And they can create an innocuous looking web site which causes anyone viewing it to make arbitrary cross-domain requests to the vulnerable application (using either the GET or the POST method).

The security impact of cross-site scripting vulnerabilities is dependent upon the nature of the vulnerable application, the kinds of data and functionality which it contains, and the other applications which belong to the same domain and organisation. If the application is used only to display non-sensitive public content, with no authentication or access control functionality, then a cross-site scripting flaw may be considered low risk. However, if the same application resides on a domain which can access cookies for other more security-critical applications, then the vulnerability could be used to attack those other applications, and so may be considered high risk. Similarly, if the organisation which owns the application is a likely target for phishing attacks, then the vulnerability could be leveraged to lend credibility to such attacks, by injecting Trojan functionality into the vulnerable application, and exploiting users' trust in the organisation in order to capture credentials for other applications which it owns. In many kinds of application, such as those providing online banking functionality, cross-site scripting should always be considered high risk.

Remediation background

In most situations where user-controllable data is copied into application responses, cross-site scripting attacks can be prevented using two layers of defences:In cases where the application's functionality allows users to author content using a restricted subset of HTML tags and attributes (for example, blog comments which allow limited formatting and linking), it is necessary to parse the supplied HTML to validate that it does not use any dangerous syntax; this is a non-trivial task.


GET / HTTP/1.1
Proxy-Connection: keep-alive
Cache-Control: max-age=0
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.16 (KHTML, like Gecko) Chrome/10.0.648.205 Safari/534.16
Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3
Cookie: JSESSIONID=dYyfN1wHZN71TmqdTHVPc5rfpmdrpWWkqQGJBTWHYGvFy6PP4kwCF9spppQp2p6T1y9LcTBvdSVRJT4zdGg0FbSwpQwRl5vyB94JHShTwbxX21bQLM8ycnhGDnyFQxbh!-2139436563; NLVisitorId=rcHW8415AZeYvnmq; NLShopperId=rcHW8415AciYvvMS; NLPromocode=438708_; promocode=; NS_VER=2011.1.0

Response (redirected)

HTTP/1.1 200 OK
Date: Mon, 25 Apr 2011 13:20:44 GMT
Server: Apache
Cache-Control: No-Cache,no-store
Pragma: No-Cache
Expires: 0
NS_RTIMER_COMPOSITE: 1564875036:73686F702D6A6176613031322E7376616C652E6E65746C65646765722E636F6D:80
X-Powered-By: Servlet/2.5 JSP/2.1
Vary: User-Agent
Content-Type: text/html; charset=utf-8
Content-Length: 54762

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>ESET Shopping Cart - ESET North America</title>

<script type="text/javascript">
var gaJsHost = (("https:" =
<input type='hidden' name='referer' value=''style='x:expression(alert(1))'be136aaa48c=1&6483e%27style%3d%27x%3aexpression%28alert%281%29%29%27be136aaa48c=1&qtyadd=1&n=1&mboxSession=1303736347554-914602&ext=T&Submit.x=43&productId=1650&Submit.y=8'>

Report generated by XSS.CX at Mon Apr 25 09:29:06 CDT 2011.