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 REST URL parameter 3 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload d2f08"><a>5ef55932490 was submitted in the REST URL parameter 3. This input was echoed unmodified in the application's response.
This behaviour demonstrates that it is possible to inject new HTML tags into the returned document. An attempt was made to identify a full proof-of-concept attack for injecting arbitrary JavaScript but this was not successful. You should manually examine the application's behaviour and attempt to identify any unusual input validation or other obstacles that may be in place.
Request
GET /articles/141112/20110504d2f08"><a>5ef55932490/valueclick-upgrade-jefferies-earnings-estimates-price-target-buy-rating-nasdaq-stock-market-fundamen.htm HTTP/1.1 Host: www.ibtimes.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.1 200 OK Date: Mon, 29 Aug 2011 01:33:46 GMT Server: Apache/2.2.3 (CentOS) X-Powered-By: PHP/5.1.6 Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: max-age=60, private, must-revalidate Pragma: no-cache Vary: Accept-Encoding Connection: close Content-Type: text/html Content-Length: 89723
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xmlns:og="http://ogp.me/ns#" xmlns: ...[SNIP]... <input type="hidden" name="redirect" value="http://www.ibtimes.com/articles/141112/20110504d2f08"><a>5ef55932490/valueclick-upgrade-jefferies-earnings-estimates-price-target-buy-rating-nasdaq-stock-market-fundamen.html" id="redirect" /> ...[SNIP]...
1.2. http://www.ibtimes.com/articles/141112/20110504/valueclick-upgrade-jefferies-earnings-estimates-price-target-buy-rating-nasdaq-stock-market-fundamen.htm [name of an arbitrarily supplied request parameter]previous
The name of an arbitrarily supplied request parameter is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 89dc0"><script>alert(1)</script>434f5dc326d was submitted in the name of an arbitrarily supplied request 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.
Request
GET /articles/141112/20110504/valueclick-upgrade-jefferies-earnings-estimates-price-target-buy-rating-nasdaq-stock-market-fundamen.htm?89dc0"><script>alert(1)</script>434f5dc326d=1 HTTP/1.1 Host: www.ibtimes.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.1 200 OK Date: Mon, 29 Aug 2011 01:33:39 GMT Server: Apache/2.2.3 (CentOS) X-Powered-By: PHP/5.1.6 Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: max-age=60, private, must-revalidate Pragma: no-cache Vary: Accept-Encoding Connection: close Content-Type: text/html Content-Length: 89344
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xmlns:og="http://ogp.me/ns#" xmlns: ...[SNIP]... <input type="hidden" name="redirect" value="http://www.ibtimes.com/articles/141112/20110504/valueclick-upgrade-jefferies-earnings-estimates-price-target-buy-rating-nasdaq-stock-market-fundamen.htm?89dc0"><script>alert(1)</script>434f5dc326d=1l" id="redirect" /> ...[SNIP]...
The application publishes a Flash cross-domain policy which allows access from any domain.
Allowing access from all domains means that any domain can perform two-way interaction with this application. Unless the application consists entirely of unprotected public content, this policy is likely to present a significant security risk.
Issue background
The Flash cross-domain policy controls whether Flash client components running on other domains can perform two-way interaction with the domain which publishes the policy. If another domain is allowed by the policy, then that domain can potentially attack users of the application. If a user is logged in to the application, and visits a domain allowed by the policy, then any malicious content running on that domain can potentially gain full access to the application within the security context of the logged in user.
Even if an allowed domain is not overtly malicious in itself, security vulnerabilities within that domain could potentially be leveraged by a third-party attacker to exploit the trust relationship and attack the application which allows access.
Issue remediation
You should review the domains which are allowed by the Flash cross-domain policy and determine whether it is appropriate for the application to fully trust both the intentions and security posture of those domains.
Request
GET /crossdomain.xml HTTP/1.0 Host: www.ibtimes.com
Response
HTTP/1.1 200 OK Date: Mon, 29 Aug 2011 01:33:33 GMT Server: Apache/2.2.3 (CentOS) X-Powered-By: PHP/5.1.6 Cache-Control: max-age=60, private, must-revalidate Expires: Mon, 29 Aug 2011 02:33:33 GMT Vary: Accept-Encoding Content-Length: 199 Connection: close Content-Type: text/xml
The response dynamically includes the following scripts from other domains:
http://edge.quantserve.com/quant.js
http://js.bizographics.com/convert_data.js
http://platform.linkedin.com/in.js
http://platform.twitter.com/widgets.js
http://www.statcounter.com/counter/counter.js
https://apis.google.com/js/plusone.js
Issue background
When an application includes a script from an external domain, this script is executed by the browser within the security context of the invoking application. The script can therefore do anything that the application's own scripts can do, such as accessing application data and performing actions within the context of the current user.
If you include a script from an external domain, then you are trusting that domain with the data and functionality of your application, and you are trusting the domain's own security to prevent an attacker from modifying the script to perform malicious actions within your application.
Issue remediation
Scripts should not be included from untrusted domains. If you have a requirement which a third-party script appears to fulfil, then you should ideally copy the contents of that script onto your own domain and include it from there. If that is not possible (e.g. for licensing reasons) then you should consider reimplementing the script's functionality within your own code.
Request
GET /articles/141112/20110504/valueclick-upgrade-jefferies-earnings-estimates-price-target-buy-rating-nasdaq-stock-market-fundamen.htm HTTP/1.1 Host: www.ibtimes.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.1 200 OK Date: Mon, 29 Aug 2011 01:33:33 GMT Server: Apache/2.2.3 (CentOS) X-Powered-By: PHP/5.1.6 Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: max-age=60, private, must-revalidate Pragma: no-cache Vary: Accept-Encoding Connection: close Content-Type: text/html Content-Length: 89258
The file robots.txt is used to give instructions to web robots, such as search engine crawlers, about locations within the web site which robots are allowed, or not allowed, to crawl and index.
The presence of the robots.txt does not in itself present any kind of security vulnerability. However, it is often used to identify restricted or private areas of a site's contents. The information in the file may therefore help an attacker to map out the site's contents, especially if some of the locations identified are not linked from elsewhere in the site. If the application relies on robots.txt to protect access to these areas, and does not enforce proper access control over them, then this presents a serious vulnerability.
Issue remediation
The robots.txt file is not itself a security threat, and its correct use can represent good practice for non-security reasons. You should not assume that all web robots will honour the file's instructions. Rather, assume that attackers will pay close attention to any locations identified in the file. Do not rely on robots.txt to provide any kind of protection over unauthorised access.
