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 organization. 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 organization 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 organization 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 sanitized.
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://blog.linkedin.com/2011/01/25/linkedin-swarm/ [name of an arbitrarily supplied request parameter]next
Summary
Severity:
High
Confidence:
Certain
Host:
http://blog.linkedin.com
Path:
/2011/01/25/linkedin-swarm/
Issue detail
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 12740"><script>alert(1)</script>89ac18eef71 was submitted in the name of an arbitrarily supplied request parameter. This input was echoed as 12740\"><script>alert(1)</script>89ac18eef71 in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
<!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml" dir="ltr" lang="en-US"> <head profile="http://gmpg.org/xfn/11"> <title>The LinkedIn Blog » LinkedIn is ...buzzing... with activi ...[SNIP]... <script type="IN/Share" data-url="http://blog.linkedin.com/2011/01/25/linkedin-swarm/?12740\"><script>alert(1)</script>89ac18eef71=1" data-counter="top"> ...[SNIP]...
1.2. http://blog.linkedin.com/2011/01/26/linkedin-promotions-data/ [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://blog.linkedin.com
Path:
/2011/01/26/linkedin-promotions-data/
Issue detail
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 dfe62"><script>alert(1)</script>b8df7e49736 was submitted in the name of an arbitrarily supplied request parameter. This input was echoed as dfe62\"><script>alert(1)</script>b8df7e49736 in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
<!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml" dir="ltr" lang="en-US"> <head profile="http://gmpg.org/xfn/11"> <title>The LinkedIn Blog » Level Up! How Millennials are Changin ...[SNIP]... <script type="IN/Share" data-url="http://blog.linkedin.com/2011/01/26/linkedin-promotions-data/?dfe62\"><script>alert(1)</script>b8df7e49736=1" data-counter="top"> ...[SNIP]...
1.3. http://blog.linkedin.com/2011/12/22/linkedin-today-2011/ [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://blog.linkedin.com
Path:
/2011/12/22/linkedin-today-2011/
Issue detail
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 b2aea"><script>alert(1)</script>e00d868ac19 was submitted in the name of an arbitrarily supplied request parameter. This input was echoed as b2aea\"><script>alert(1)</script>e00d868ac19 in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
<!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml" dir="ltr" lang="en-US"> <head profile="http://gmpg.org/xfn/11"> <title>The LinkedIn Blog » The Most Popular Stories on LinkedIn ...[SNIP]... <script type="IN/Share" data-url="http://blog.linkedin.com/2011/12/22/linkedin-today-2011/?b2aea\"><script>alert(1)</script>e00d868ac19=1" data-counter="top"> ...[SNIP]...
1.4. http://blog.linkedin.com/2011/12/23/linkedin-blog-2011/ [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://blog.linkedin.com
Path:
/2011/12/23/linkedin-blog-2011/
Issue detail
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 44950"><script>alert(1)</script>8cdfd362591 was submitted in the name of an arbitrarily supplied request parameter. This input was echoed as 44950\"><script>alert(1)</script>8cdfd362591 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 value of the background request parameter is copied into the HTML document as plain text between tags. The payload f303a<script>alert(1)</script>2bffe30da4d was submitted in the background 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.
The value of the infobackground request parameter is copied into the HTML document as plain text between tags. The payload 26be2<script>alert(1)</script>43636c77d0f was submitted in the infobackground 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.
The value of the infocolor request parameter is copied into the HTML document as plain text between tags. The payload 64271<script>alert(1)</script>74b2636ac13 was submitted in the infocolor 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.
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 fulfill, 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.
<!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml" dir="ltr" lang="en-US"> <head profile="http://gmpg.org/xfn/11"> <title>The LinkedIn Blog » The Most Popular Stories on LinkedIn ...[SNIP]... </a><script type="text/javascript" src="//platform.twitter.com/widgets.js"></script> ...[SNIP]...
The TRACE method is designed for diagnostic purposes. If enabled, the web server will respond to requests which use the TRACE method by echoing in its response the exact request which was received.
Although this behavior is apparently harmless in itself, it can sometimes be leveraged to support attacks against other application users. If an attacker can find a way of causing a user to make a TRACE request, and can retrieve the response to that request, then the attacker will be able to capture any sensitive data which is included in the request by the user's browser, for example session cookies or credentials for platform-level authentication. This may exacerbate the impact of other vulnerabilities, such as cross-site scripting.
Issue remediation
The TRACE method should be disabled on the web server.
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 honor 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 unauthorized access.
Request
GET /robots.txt HTTP/1.0 Host: blog.linkedin.com
Response
HTTP/1.0 200 OK Served-By: Joyent Server: Apache Vary: Accept-Encoding Content-Type: text/plain; charset=utf-8 Date: Sun, 08 Jan 2012 02:25:18 GMT X-Pingback: http://blog.linkedin.com/xmlrpc.php Connection: close Content-Length: 24
User-agent: * Disallow:
Report generated by XSS.Cx at Wed Aug 08 11:02:14 EDT 2012.