XSS, Cross Site Scripting, Blekko.com, CWE-79, CAPEC-86, DORK

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

Report generated by XSS.CX at Thu Mar 17 08:57:42 CDT 2011.

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1. Cross-site scripting (reflected)

2. Cookie without HttpOnly flag set

3. Cross-domain script include

4. Content type incorrectly stated

1. Cross-site scripting (reflected) next

Summary

Severity:	High
Confidence:	Certain
Host:	http://blekko.com
Path:	/autocomplete

Issue detail

The value of the query request parameter is copied into the HTML document as plain text between tags. The payload d649e<script>alert(1)</script>19f19cf1ce4 was submitted in the query 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.

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.

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.

Request

GET /autocomplete?query=http%3A%2F%2Fxs+%2Fseo3d73f%3Cscript%3Ealert(1)%3C/script%3E63bc5c45e1dd649e<script>alert(1)</script>19f19cf1ce4 HTTP/1.1
Host: blekko.com
Proxy-Connection: keep-alive
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.16 (KHTML, like Gecko) Chrome/10.0.648.133 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: domainseo-tab=domaincont-1; v=3; fbl=2; sessionid=382288941; suggestedSlashtagsList=1

Response

HTTP/1.1 200 OK
Server: nginx
Date: Wed, 16 Mar 2011 21:41:37 GMT
Content-Type: text/plain; charset=utf-8
Connection: keep-alive
Keep-Alive: timeout=15
Vary: Accept-Encoding
Cache-Control: max-age=43200
Expires: Thu, 17 Mar 2011 09:41:37 GMT
Vary: Accept-Encoding
X-Blekko-PT: 39976c5bed62cb4d4d21f8e7113f6dfe
Content-Length: 125

{"suggestions":[],"query":"http://xs /seo3d73f<script>alert(1)</script>63bc5c45e1dd649e<script>alert(1)</script>19f19cf1ce4"}

2. Cookie without HttpOnly flag set previous next

Summary

Severity:	Low
Confidence:	Firm
Host:	http://blekko.com
Path:	/ws/michelangelo+/%27%22--%3E%3C/style%3E%3C/script%3E%3Cscript%3Ealert(0x00068B)%3C/script%3E

Issue detail

The following cookie was issued by the application and does not have the HttpOnly flag set:

sessionid=684373293; 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.

Request

GET /ws/michelangelo+/%27%22--%3E%3C/style%3E%3C/script%3E%3Cscript%3Ealert(0x00068B)%3C/script%3E HTTP/1.1
Host: blekko.com
Proxy-Connection: keep-alive
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.16 (KHTML, like Gecko) Chrome/10.0.648.133 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: domainseo-tab=domaincont-1; v=3; fbl=2

Response

3. Cross-domain script include previous next

Summary

Severity:	Information
Confidence:	Certain
Host:	http://blekko.com
Path:	/ws/michelangelo+/%27%22--%3E%3C/style%3E%3C/script%3E%3Cscript%3Ealert(0x00068B)%3C/script%3E

Issue detail

The response dynamically includes the following scripts from other domains:

http://a.blekko-img.com/045/gz/2d59ccdc20e73672_jquery.json-2.2.min.js
http://a.blekko-img.com/045/gz/386aa2239672201a_search.js
http://a.blekko-img.com/045/gz/c89ba3a4becb3add_blekko.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

Response

HTTP/1.1 200 OK
Server: nginx
Date: Wed, 16 Mar 2011 21:40:38 GMT
Content-Type: text/html; charset=UTF-8
Connection: keep-alive
Keep-Alive: timeout=15
Set-Cookie: fbl=2; path=/; expires=Sat, 13 Mar 2021 21:40:37 GMT
Set-Cookie: sessionid=684373293; path=/
Cache-Control: no-cache, max-age=0
Expires: -1
Pragma: no-cache
X-Blekko-QF: Qcehq
X-Blekko-PT: fc99475cd8837f1ece008579ffb3b7d6
Content-Length: 89706

<!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:fb="http://www.facebook.com/2
...[SNIP]...
</div>
<script type="text/javascript" src="http://a.blekko-img.com/045/gz/c89ba3a4becb3add_blekko.js"></script>
<script type="text/javascript" src="http://a.blekko-img.com/045/gz/2d59ccdc20e73672_jquery.json-2.2.min.js"></script>
<script type="text/javascript" src="http://a.blekko-img.com/045/gz/386aa2239672201a_search.js"></script>
...[SNIP]...

4. Content type incorrectly stated previous

Summary

Severity:	Information
Confidence:	Firm
Host:	http://blekko.com
Path:	/autocomplete

Issue detail

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 JSON.

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.

Request

GET /autocomplete?query=http%3A%2F%2Fxs+%2Fseo3d73f%3Cscript%3Ealert(1)%3C/script%3E63bc5c45e1d HTTP/1.1
Host: blekko.com
Proxy-Connection: keep-alive
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.16 (KHTML, like Gecko) Chrome/10.0.648.133 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: domainseo-tab=domaincont-1; v=3; fbl=2; sessionid=382288941; suggestedSlashtagsList=1

Response

HTTP/1.1 200 OK
Server: nginx
Date: Wed, 16 Mar 2011 21:41:13 GMT
Content-Type: text/plain; charset=utf-8
Connection: keep-alive
Keep-Alive: timeout=15
Cache-Control: max-age=43200
Expires: Thu, 17 Mar 2011 09:41:13 GMT
Vary: Accept-Encoding
Content-Length: 84
X-Blekko-PT: aeacb164eb790d8186558690ca492000

{"suggestions":[],"query":"http://xs /seo3d73f<script>alert(1)</script>63bc5c45e1d"}

Report generated by XSS.CX at Thu Mar 17 08:57:42 CDT 2011.