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.
Issue remediation
In most situations where user-controllable data is copied into application responses, cross-site scripting attacks can be prevented using two layers of defences:
Input should be validated as strictly as possible on arrival, given the kind of content which it is expected to contain. For example, personal names should consist of alphabetical and a small range of typographical characters, and be relatively short; a year of birth should consist of exactly four numerals; email addresses should match a well-defined regular expression. Input which fails the validation should be rejected, not sanitised.
User input should be HTML-encoded at any point where it is copied into application responses. All HTML metacharacters, including < > " ' and =, should be replaced with the corresponding HTML entities (< > etc).
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.
The value of the txtComments request parameter is copied into the HTML document as plain text between tags. The payload 5219b<script>alert(1)</script>802bfa23598 was submitted in the txtComments parameter. This input was echoed unmodified 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 value of the txtEmail request parameter is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 4ca4d"><script>alert(1)</script>08a208d96a9 was submitted in the txtEmail parameter. This input was echoed unmodified 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 value of the txtName request parameter is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 63b2a"><script>alert(1)</script>432c2a8d3ff was submitted in the txtName parameter. This input was echoed unmodified 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 following cookie was issued by the application and does not have the HttpOnly flag set:
PHPSESSID=jmar79ddqukv2hdfk8n06g3lv7; path=/
The cookie appears to contain a session token, which may increase the risk associated with this issue. You should review the contents of the cookie to determine its function.
Issue background
If the HttpOnly attribute is set on a cookie, then the cookie's value cannot be read or set by client-side JavaScript. This measure can prevent certain client-side attacks, such as cross-site scripting, from trivially capturing the cookie's value via an injected script.
Issue remediation
There is usually no good reason not to set the HttpOnly flag on all cookies. Unless you specifically require legitimate client-side scripts within your application to read or set a cookie's value, you should set the HttpOnly flag by including this attribute within the relevant Set-cookie directive.
You should be aware that the restrictions imposed by the HttpOnly flag can potentially be circumvented in some circumstances, and that numerous other serious attacks can be delivered by client-side script injection, aside from simple cookie stealing.
Server-side source code may contain sensitive information which can help an attacker formulate attacks against the application.
Issue remediation
Server-side source code is normally disclosed to clients as a result of typographical errors in scripts or because of misconfiguration, such as failing to grant executable permissions to a script or directory. You should review the cause of the code disclosure and prevent it from happening.
The application appears to disclose some server-side source code written in PHP.
Request
GET /includes/jquery-1.4.4.min.js HTTP/1.1 Host: cat.net Proxy-Connection: keep-alive Referer: http://cat.net/ User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.112 Safari/535.1 Accept: */* 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
Response
HTTP/1.1 200 OK Date: Thu, 18 Aug 2011 17:34:21 GMT Server: Apache/2.2.3 (Red Hat) Last-Modified: Wed, 05 Jan 2011 12:55:06 GMT ETag: "3608006-133ec-49918e4ef5e80" Accept-Ranges: bytes Content-Length: 78828 Connection: close Content-Type: application/x-javascript
/*! * jQuery JavaScript Library v1.4.4 * http://jquery.com/ * * Copyright <?php echo date('Y');?>, John Resig * Dual licensed under the MIT or GPL Version 2 licenses. * http://jquery.org/license * * Includes Sizzle.js * http://sizzlejs.com/ * Copyright <?php echo date('Y');?>, The Dojo Foundation * Released under the MIT, BSD, and GPL Licenses. * * Date: Thu Nov 11 19:04:53 <?php echo date('Y');?> -0500 */ (function(E,B){function ka(a,b,d){if(d===B&&a.nodeType===1){d=a.getAttribute("data-"+b);if(typeof d==="string"){try{d=d==="true"?true:d==="false"?false:d==="null"?null:!c.isNaN(d)?parseFlo ...[SNIP]...
The application appears to disclose some server-side source code written in PHP.
Request
GET /includes/jquery.corner.js HTTP/1.1 Host: cat.net Proxy-Connection: keep-alive Referer: http://cat.net/ User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.112 Safari/535.1 Accept: */* 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
Response
HTTP/1.1 200 OK Date: Thu, 18 Aug 2011 17:34:21 GMT Server: Apache/2.2.3 (Red Hat) Last-Modified: Wed, 05 Jan 2011 12:55:05 GMT ETag: "3608007-2cb8-49918e4e01c40" Accept-Ranges: bytes Content-Length: 11448 Connection: close Content-Type: application/x-javascript
/*! * jQuery corner plugin: simple corner rounding * Examples and documentation at: http://jquery.malsup.com/corner/ * version 2.11 (15-JUN- <?php echo date('Y');?>) * Requires jQuery v1.3.2 or later * Dual licensed under the MIT and GPL licenses: * http://www.opensource.org/licenses/mit-license.php * http://www.gnu.org/licenses/gpl.html * Authors: Dave ...[SNIP]...
The response contains the following Content-type statement:
Content-Type: text/plain; charset=UTF-8
The response states that it contains plain text. However, it actually appears to contain unrecognised content.
Issue background
If a web response specifies an incorrect content type, then browsers may process the response in unexpected ways. If the specified content type is a renderable text-based format, then the browser will usually attempt to parse and render the response in that format. If the specified type is an image format, then the browser will usually detect the anomaly and will analyse the actual content and attempt to determine its MIME type. Either case can lead to unexpected results, and if the content contains any user-controllable data may lead to cross-site scripting or other client-side vulnerabilities.
In most cases, the presence of an incorrect content type statement does not constitute a security flaw, particularly if the response contains static content. You should review the contents of the response and the context in which it appears to determine whether any vulnerability exists.
Issue remediation
For every response containing a message body, the application should include a single Content-type header which correctly and unambiguously states the MIME type of the content in the response body.
