XSS, pixel.fetchback.com, Cross Site Scripting, CWe-79, CAPEC-86

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

Report generated by CloudScan Vulnerability Crawler at Sun Feb 27 16:16:27 CST 2011.

1. Cross-site scripting (reflected)

2. Referer-dependent response

3. Cookie scoped to parent domain

3.1. http://pixel.fetchback.com/serve/fb/pdc

3.2. http://pixel.fetchback.com/serve/fb/ver

4. Cookie without HttpOnly flag set

4.1. http://pixel.fetchback.com/serve/fb/pdc

4.2. http://pixel.fetchback.com/serve/fb/ver

1. Cross-site scripting (reflected) next

Summary

Severity:	High
Confidence:	Certain
Host:	http://pixel.fetchback.com
Path:	/serve/fb/pdc

Issue detail

The value of the name request parameter is copied into the HTML document as plain text between tags. The payload defbc<x%20style%3dx%3aexpression(alert(1))>4a37e91db64 was submitted in the name parameter. This input was echoed as defbc<x style=x:expression(alert(1))>4a37e91db64 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.

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 defenses:

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 /serve/fb/pdc?cat=&name=landingdefbc<x%20style%3dx%3aexpression(alert(1))>4a37e91db64&sid=2002 HTTP/1.1
Host: pixel.fetchback.com
Proxy-Connection: keep-alive
Referer: http://www.nfl.com/
Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.13 (KHTML, like Gecko) Chrome/9.0.597.98 Safari/534.13
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: Wed, 16 Feb 2011 13:18:50 GMT
Server: Apache/2.2.3 (CentOS)
Set-Cookie: cmp=1_1297862330; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:50 GMT; Path=/
Set-Cookie: uid=1_1297862330_1297862330748:1987892397597993; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:50 GMT; Path=/
Set-Cookie: kwd=1_1297862330; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:50 GMT; Path=/
Set-Cookie: sit=1_1297862330; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:50 GMT; Path=/
Set-Cookie: cre=1_1297862330; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:50 GMT; Path=/
Set-Cookie: bpd=1_1297862330; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:50 GMT; Path=/
Set-Cookie: apd=1_1297862330; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:50 GMT; Path=/
Set-Cookie: scg=1_1297862330; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:50 GMT; Path=/
Set-Cookie: ppd=1_1297862330; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:50 GMT; Path=/
Set-Cookie: afl=1_1297862330; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:50 GMT; Path=/
Cache-Control: max-age=0, no-store, must-revalidate, no-cache
Expires: Wed, 16 Feb 2011 13:18:50 GMT
Pragma: no-cache
P3P: policyref="/w3c/p3p.xml", CP="NOI DSP COR NID CURa ADMa DEVa PSAa PSDa OUR BUS COM INT OTC PUR STA"
Vary: Accept-Encoding
Connection: close
Content-Type: text/html; charset=UTF-8
Content-Length: 90

2. Referer-dependent response previous next

Summary

Severity:	Information
Confidence:	Firm
Host:	http://pixel.fetchback.com
Path:	/serve/fb/pdc

Issue description

The application's responses appear to depend systematically on the presence or absence of the Referer header in requests. This behaviour does not necessarily constitute a security vulnerability, and you should investigate the nature of and reason for the differential responses to determine whether a vulnerability is present.

Common explanations for Referer-dependent responses include:

Referer-based access controls, where the application assumes that if you have arrived from one privileged location then you are authorised to access another privileged location. These controls can be trivially defeated by supplying an accepted Referer header in requests for the vulnerable function.
Attempts to prevent cross-site request forgery attacks by verifying that requests to perform privileged actions originated from within the application itself and not from some external location. Such defenses are not robust - methods have existed through which an attacker can forge or mask the Referer header contained within a target user's requests, by leveraging client-side technologies such as Flash and other techniques.
Delivery of Referer-tailored content, such as welcome messages to visitors from specific domains, search-engine optimisation (SEO) techniques, and other ways of tailoring the user's experience. Such behaviours often have no security impact; however, unsafe processing of the Referer header may introduce vulnerabilities such as SQL injection and cross-site scripting. If parts of the document (such as META keywords) are updated based on search engine queries contained in the Referer header, then the application may be vulnerable to persistent code injection attacks, in which search terms are manipulated to cause malicious content to appear in responses served to other application users.

Issue remediation

The Referer header is not a robust foundation on which to build any security measures, such as access controls or defenses against cross-site request forgery. Any such measures should be replaced with more secure alternatives that are not vulnerable to Referer spoofing.

If the contents of responses is updated based on Referer data, then the same defenses against malicious input should be employed here as for any other kinds of user-supplied data.

Request 1

GET /serve/fb/pdc?cat=&name=landing&sid=2002 HTTP/1.1
Host: pixel.fetchback.com
Proxy-Connection: keep-alive
Referer: http://www.nfl.com/
Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.13 (KHTML, like Gecko) Chrome/9.0.597.98 Safari/534.13
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 1

HTTP/1.1 200 OK
Date: Wed, 16 Feb 2011 13:18:41 GMT
Server: Apache/2.2.3 (CentOS)
Set-Cookie: cmp=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
Set-Cookie: uid=1_1297862321_1297862321600:4263790046630086; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
Set-Cookie: kwd=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
Set-Cookie: sit=1_1297862321_2002:0:0; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
Set-Cookie: cre=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
Set-Cookie: bpd=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
Set-Cookie: apd=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
Set-Cookie: scg=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
Set-Cookie: ppd=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
Set-Cookie: afl=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
Cache-Control: max-age=0, no-store, must-revalidate, no-cache
Expires: Wed, 16 Feb 2011 13:18:41 GMT
Pragma: no-cache
P3P: policyref="/w3c/p3p.xml", CP="NOI DSP COR NID CURa ADMa DEVa PSAa PSDa OUR BUS COM INT OTC PUR STA"
Vary: Accept-Encoding
Connection: close
Content-Type: text/html; charset=UTF-8
Content-Length: 570


<img src='http://pixel.fetchback.com/serve/fb/ver?uatFilter=false&fb_key=pixel.fetchback.comcat%3D%26name%3Dlanding%26sid%3D2002http%3A%2F%2Fwww.nfl.com%2F+%2Fserve%2Ffb%2Fpdc&cat=&sid=2002&name=landing&uid=1297862321600%3A4263790046630086&crv=0.0&oid=Unknown' border='0' width='1' height='1' alt='' />
<![if !IE 6]>
<script language='javascript' type='text/javascript'>
function timeout(){location.replace('http://pixel.fetchback.com/timeout.html');}
setTimeout(timeout,2001);
</script>
<![endif]>

Request 2

GET /serve/fb/pdc?cat=&name=landing&sid=2002 HTTP/1.1
Host: pixel.fetchback.com
Proxy-Connection: keep-alive
Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.13 (KHTML, like Gecko) Chrome/9.0.597.98 Safari/534.13
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 2

HTTP/1.1 200 OK
Date: Wed, 16 Feb 2011 13:18:45 GMT
Server: Apache/2.2.3 (CentOS)
Set-Cookie: cmp=1_1297862325; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:45 GMT; Path=/
Set-Cookie: uid=1_1297862325_1297862325759:0168104296241760; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:45 GMT; Path=/
Set-Cookie: kwd=1_1297862325; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:45 GMT; Path=/
Set-Cookie: sit=1_1297862325_2002:0:0; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:45 GMT; Path=/
Set-Cookie: cre=1_1297862325; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:45 GMT; Path=/
Set-Cookie: bpd=1_1297862325; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:45 GMT; Path=/
Set-Cookie: apd=1_1297862325; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:45 GMT; Path=/
Set-Cookie: scg=1_1297862325; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:45 GMT; Path=/
Set-Cookie: ppd=1_1297862325; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:45 GMT; Path=/
Set-Cookie: afl=1_1297862325; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:45 GMT; Path=/
Cache-Control: max-age=0, no-store, must-revalidate, no-cache
Expires: Wed, 16 Feb 2011 13:18:45 GMT
Pragma: no-cache
P3P: policyref="/w3c/p3p.xml", CP="NOI DSP COR NID CURa ADMa DEVa PSAa PSDa OUR BUS COM INT OTC PUR STA"
Vary: Accept-Encoding
Connection: close
Content-Type: text/html; charset=UTF-8
Content-Length: 543


<img src='http://pixel.fetchback.com/serve/fb/ver?uatFilter=false&fb_key=pixel.fetchback.comcat%3D%26name%3Dlanding%26sid%3D2002+%2Fserve%2Ffb%2Fpdc&cat=&sid=2002&name=landing&uid=1297862325759%3A0168104296241760&crv=0.0&oid=Unknown' border='0' width='1' height='1' alt='' />
<![if !IE 6]>
<script language='javascript' type='text/javascript'>
function timeout(){location.replace('http://pixel.fetchback.com/timeout.html');}
setTimeout(timeout,2001);
</script>
<![endif]>

3. Cookie scoped to parent domain previous next
There are 2 instances of this issue:

/serve/fb/pdc
/serve/fb/ver

Issue background

A cookie's domain attribute determines which domains can access the cookie. Browsers will automatically submit the cookie in requests to in-scope domains, and those domains will also be able to access the cookie via JavaScript. If a cookie is scoped to a parent domain, then that cookie will be accessible by the parent domain and also by any other subdomains of the parent domain. If the cookie contains sensitive data (such as a session token) then this data may be accessible by less trusted or less secure applications residing at those domains, leading to a security compromise.

Issue remediation

By default, cookies are scoped to the issuing domain and all subdomains. If you remove the explicit domain attribute from your Set-cookie directive, then the cookie will have this default scope, which is safe and appropriate in most situations. If you particularly need a cookie to be accessible by a parent domain, then you should thoroughly review the security of the applications residing on that domain and its subdomains, and confirm that you are willing to trust the people and systems which support those applications.

3.1. http://pixel.fetchback.com/serve/fb/pdc next

Summary

Severity:	Information
Confidence:	Certain
Host:	http://pixel.fetchback.com
Path:	/serve/fb/pdc

Issue detail

The following cookies were issued by the application and is scoped to a parent of the issuing domain:

cmp=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
uid=1_1297862321_1297862321600:4263790046630086; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
kwd=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
sit=1_1297862321_2002:0:0; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
cre=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
bpd=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
apd=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
scg=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
ppd=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
afl=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/

The cookies do not appear to contain session tokens, which may reduce the risk associated with this issue. You should review the contents of the cookies to determine their function.

Request

Response

3.2. http://pixel.fetchback.com/serve/fb/ver previous next

Summary

Severity:	Information
Confidence:	Certain
Host:	http://pixel.fetchback.com
Path:	/serve/fb/ver

Issue detail

The following cookies were issued by the application and is scoped to a parent of the issuing domain:

uid=1_1297862321_1297862321306:0415785655118336; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
cre=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/

The cookies do not appear to contain session tokens, which may reduce the risk associated with this issue. You should review the contents of the cookies to determine their function.

Request

GET /serve/fb/ver?uatFilter=false&fb_key=pixel.fetchback.comcat%3D%26name%3Dlanding%26sid%3D2002http%3A%2F%2Fwww.nfl.com%2F+%2Fserve%2Ffb%2Fpdc&cat=&sid=2002&name=landing&uid=1297862321306%3A0415785655118336&crv=0.0&oid=Unknown HTTP/1.1
Host: pixel.fetchback.com
Proxy-Connection: keep-alive
Referer: http://pixel.fetchback.com/serve/fb/pdc?cat=&name=landing&sid=2002
Accept: */*
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.13 (KHTML, like Gecko) Chrome/9.0.597.98 Safari/534.13
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: cmp=1_1297862321; uid=1_1297862321_1297862321306:0415785655118336; kwd=1_1297862321; sit=1_1297862321_2002:0:0; cre=1_1297862321; bpd=1_1297862321; apd=1_1297862321; scg=1_1297862321; ppd=1_1297862321; afl=1_1297862321

Response

HTTP/1.1 200 OK
Date: Wed, 16 Feb 2011 13:18:41 GMT
Server: Apache/2.2.3 (CentOS)
Set-Cookie: uid=1_1297862321_1297862321306:0415785655118336; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
Set-Cookie: cre=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
Cache-Control: max-age=0, no-store, must-revalidate, no-cache
Expires: Wed, 16 Feb 2011 13:18:41 GMT
Pragma: no-cache
P3P: policyref="/w3c/p3p.xml", CP="NOI DSP COR NID CURa ADMa DEVa PSAa PSDa OUR BUS COM INT OTC PUR STA"
Vary: Accept-Encoding
Connection: close
Content-Type: image/gif
Content-Length: 43

GIF89a.............!.......,...........D..;

4. Cookie without HttpOnly flag set previous
There are 2 instances of this issue:

/serve/fb/pdc
/serve/fb/ver

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.

4.1. http://pixel.fetchback.com/serve/fb/pdc previous next

Summary

Severity:	Information
Confidence:	Certain
Host:	http://pixel.fetchback.com
Path:	/serve/fb/pdc

Issue detail

The following cookies were issued by the application and do not have the HttpOnly flag set:

cmp=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
uid=1_1297862321_1297862321600:4263790046630086; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
kwd=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
sit=1_1297862321_2002:0:0; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
cre=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
bpd=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
apd=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
scg=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
ppd=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
afl=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/

The cookies do not appear to contain session tokens, which may reduce the risk associated with this issue. You should review the contents of the cookies to determine their function.

Request

Response

4.2. http://pixel.fetchback.com/serve/fb/ver previous

Summary

Severity:	Information
Confidence:	Certain
Host:	http://pixel.fetchback.com
Path:	/serve/fb/ver

Issue detail

The following cookies were issued by the application and do not have the HttpOnly flag set:

uid=1_1297862321_1297862321306:0415785655118336; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/
cre=1_1297862321; Domain=.fetchback.com; Expires=Mon, 15-Feb-2016 13:18:41 GMT; Path=/

The cookies do not appear to contain session tokens, which may reduce the risk associated with this issue. You should review the contents of the cookies to determine their function.

Request

Response

Report generated by CloudScan Vulnerability Crawler at Sun Feb 27 16:16:27 CST 2011.