XSS, Cross Site Scripting, CWE-79, CAPEC-86, fonts.googleapis.com

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

Report generated by CloudScan Vulnerability Crawler at Fri Feb 25 15:03:54 CST 2011.

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1. Cross-site scripting (reflected)

2. Robots.txt file


1. Cross-site scripting (reflected)  next

Summary

Severity:   High
Confidence:   Certain
Host:   http://fonts.googleapis.com
Path:   /css

Issue detail

The value of the family request parameter is copied into the HTML document as plain text between tags. The payload 94c8b<script>alert(1)</script>423290838b3 was submitted in the family 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 defenses: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 /css?family=94c8b<script>alert(1)</script>423290838b3&subset=latin HTTP/1.1
Host: fonts.googleapis.com
Proxy-Connection: keep-alive
Referer: http://tools.google.com/chrome/intl/en/welcome.html
Accept: text/css,*/*;q=0.1
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
Content-Type: text/css; charset=UTF-8
Expires: Tue, 15 Feb 2011 21:08:54 GMT
Date: Tue, 15 Feb 2011 21:08:54 GMT
Cache-Control: private, max-age=86400
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-XSS-Protection: 1; mode=block
Server: GSE
Content-Length: 114

/* 94c8b<script>alert(1)</script>423290838b3 (style: normal, weight: 400) is not available */
/* Not supported. */
2. Robots.txt file  previous

Summary

Severity:   Information
Confidence:   Certain
Host:   http://fonts.googleapis.com
Path:   /css

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: fonts.googleapis.com

Response

HTTP/1.0 200 OK
Content-Type: text/plain
Date: Tue, 15 Feb 2011 21:08:48 GMT
Expires: Tue, 15 Feb 2011 21:08:48 GMT
Cache-Control: private, max-age=0
X-Content-Type-Options: nosniff
X-Frame-Options: SAMEORIGIN
X-XSS-Protection: 1; mode=block
Server: GSE

User-agent: *
Disallow: /
Report generated by CloudScan Vulnerability Crawler at Fri Feb 25 15:03:54 CST 2011.