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.
The value of REST URL parameter 1 is copied into the HTML document as plain text between tags. The payload 7a339<script>alert(1)</script>968fcc00f04 was submitted in the REST URL parameter 1. 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.
Request
GET /favicon.ico7a339<script>alert(1)</script>968fcc00f04 HTTP/1.1 Host: flashstats.libsyn.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.13) Gecko/20110504 Namoroka/3.6.13 Accept: image/png,image/*;q=0.8,*/*;q=0.5 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 115 Proxy-Connection: keep-alive
Response
HTTP/1.0 200 OK Date: Mon, 07 Nov 2011 01:00:45 GMT Server: Apache Vary: Accept-Encoding X-Libsyn-Host: consumer-server2.libsyn.com Content-Length: 4492 Connection: close Content-Type: text/html
1.2. http://flashstats.libsyn.com/favicon.ico [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://flashstats.libsyn.com
Path:
/favicon.ico
Issue detail
The name of an arbitrarily supplied request parameter is copied into the HTML document as plain text between tags. The payload f34f4<script>alert(1)</script>256d1b1dea9 was submitted in the name of an arbitrarily supplied request 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.
Request
GET /favicon.ico?f34f4<script>alert(1)</script>256d1b1dea9=1 HTTP/1.1 Host: flashstats.libsyn.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.13) Gecko/20110504 Namoroka/3.6.13 Accept: image/png,image/*;q=0.8,*/*;q=0.5 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 115 Proxy-Connection: keep-alive
Response
HTTP/1.0 200 OK Date: Mon, 07 Nov 2011 01:07:44 GMT Server: Apache Vary: Accept-Encoding X-Libsyn-Host: consumer-server1.libsyn.com Content-Length: 4362 Connection: close Content-Type: text/html
The value of REST URL parameter 1 is copied into the HTML document as plain text between tags. The payload beec7<script>alert(1)</script>d1849083195 was submitted in the REST URL parameter 1. 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.
Request
GET /loggingbeec7<script>alert(1)</script>d1849083195/log HTTP/1.1 Host: flashstats.libsyn.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.0 200 OK Date: Mon, 07 Nov 2011 00:55:11 GMT Server: Apache X-Libsyn-Host: consumer-server2.libsyn.com Vary: Accept-Encoding Content-Length: 4480 Connection: close Content-Type: text/html
The value of REST URL parameter 2 is copied into the HTML document as plain text between tags. The payload 9c4a3<script>alert(1)</script>65867a430ff was submitted in the REST URL parameter 2. 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.
Request
GET /logging/log9c4a3<script>alert(1)</script>65867a430ff HTTP/1.1 Host: flashstats.libsyn.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.0 200 OK Date: Mon, 07 Nov 2011 00:55:12 GMT Server: Apache X-Libsyn-Host: consumer-server2.libsyn.com Vary: Accept-Encoding Content-Length: 5816 Connection: close Content-Type: text/html
1.5. http://jqueryui.com/themeroller/ [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://jqueryui.com
Path:
/themeroller/
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 a3e02"><script>alert(1)</script>99f30a038e7 was submitted in the name of an arbitrarily supplied request 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.
Request
GET /themeroller/?a3e02"><script>alert(1)</script>99f30a038e7=1 HTTP/1.1 Host: jqueryui.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.1 200 OK Server: nginx/0.7.62 Date: Mon, 07 Nov 2011 01:16:39 GMT Content-Type: text/html Connection: close X-Powered-By: PHP/5.2.4-2ubuntu5.10 X-Served-By: www3 X-Proxy: 1 Content-Length: 117289
The value of the message request parameter is copied into the HTML document as plain text between tags. The payload 6e251<script>alert(1)</script>32adcdb90a9 was submitted in the message 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.
Note that a redirection occurred between the attack request and the response containing the echoed input. It is necessary to follow this redirection for the attack to succeed. When the attack is carried out via a browser, the redirection will be followed automatically.
The value of the message request parameter is copied into the HTML document as plain text between tags. The payload d29d5<script>alert(1)</script>0920b9297ce was submitted in the message 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 REST URL parameter 1 is copied into the HTML document as plain text between tags. The payload 1435d<script>alert(1)</script>47aeccc300408d10 was submitted in the REST URL parameter 1. 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 original request used the POST method, however it was possible to convert the request to use the GET method, to enable easier demonstration and delivery of the attack.
The value of REST URL parameter 2 is copied into the HTML document as plain text between tags. The payload edfaf<script>alert(1)</script>020d68e3364e2ad2c was submitted in the REST URL parameter 2. 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 original request used the POST method, however it was possible to convert the request to use the GET method, to enable easier demonstration and delivery of the attack.
The value of REST URL parameter 1 is copied into the HTML document as plain text between tags. The payload d24a8<script>alert(1)</script>e01e658d073 was submitted in the REST URL parameter 1. 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.
Passwords submitted over an unencrypted connection are vulnerable to capture by an attacker who is suitably positioned on the network. This includes any malicious party located on the user's own network, within their ISP, within the ISP used by the application, and within the application's hosting infrastructure. Even if switched networks are employed at some of these locations, techniques exist to circumvent this defence and monitor the traffic passing through switches.
Issue remediation
The application should use transport-level encryption (SSL or TLS) to protect all sensitive communications passing between the client and the server. Communications that should be protected include the login mechanism and related functionality, and any functions where sensitive data can be accessed or privileged actions can be performed. These areas of the application should employ their own session handling mechanism, and the session tokens used should never be transmitted over unencrypted communications. If HTTP cookies are used for transmitting session tokens, then the secure flag should be set to prevent transmission over clear-text HTTP.
Most browsers have a facility to remember user credentials that are entered into HTML forms. This function can be configured by the user and also by applications which employ user credentials. If the function is enabled, then credentials entered by the user are stored on their local computer and retrieved by the browser on future visits to the same application.
The stored credentials can be captured by an attacker who gains access to the computer, either locally or through some remote compromise. Further, methods have existed whereby a malicious web site can retrieve the stored credentials for other applications, by exploiting browser vulnerabilities or through application-level cross-domain attacks.
Issue remediation
To prevent browsers from storing credentials entered into HTML forms, you should include the attribute autocomplete="off" within the FORM tag (to protect all form fields) or within the relevant INPUT tags (to protect specific individual fields).
When a web browser makes a request for a resource, it typically adds an HTTP header, called the "Referer" header, indicating the URL of the resource from which the request originated. This occurs in numerous situations, for example when a web page loads an image or script, or when a user clicks on a link or submits a form.
If the resource being requested resides on a different domain, then the Referer header is still generally included in the cross-domain request. If the originating URL contains any sensitive information within its query string, such as a session token, then this information will be transmitted to the other domain. If the other domain is not fully trusted by the application, then this may lead to a security compromise.
You should review the contents of the information being transmitted to other domains, and also determine whether those domains are fully trusted by the originating application.
Today's browsers may withhold the Referer header in some situations (for example, when loading a non-HTTPS resource from a page that was loaded over HTTPS, or when a Refresh directive is issued), but this behaviour should not be relied upon to protect the originating URL from disclosure.
Note also that if users can author content within the application then an attacker may be able to inject links referring to a domain they control in order to capture data from URLs used within the application.
Issue remediation
The application should never transmit any sensitive information within the URL query string. In addition to being leaked in the Referer header, such information may be logged in various locations and may be visible on-screen to untrusted parties.
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
GET /themeroller/ HTTP/1.1 Host: jqueryui.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.1 200 OK Server: nginx/0.7.62 Date: Mon, 07 Nov 2011 01:16:33 GMT Content-Type: text/html Connection: close X-Powered-By: PHP/5.2.4-2ubuntu5.10 X-Served-By: www3 X-Proxy: 1 Content-Length: 117175
The presence of email addresses within application responses does not necessarily constitute a security vulnerability. Email addresses may appear intentionally within contact information, and many applications (such as web mail) include arbitrary third-party email addresses within their core content.
However, email addresses of developers and other individuals (whether appearing on-screen or hidden within page source) may disclose information that is useful to an attacker; for example, they may represent usernames that can be used at the application's login, and they may be used in social engineering attacks against the organisation's personnel. Unnecessary or excessive disclosure of email addresses may also lead to an increase in the volume of spam email received.
Issue remediation
You should review the email addresses being disclosed by the application, and consider removing any that are unnecessary, or replacing personal addresses with anonymous mailbox addresses (such as helpdesk@example.com).
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html la ...[SNIP]... .push(['_linkByPost',this]); } }); //check for maintence mode if (maintenance_mode){ $('#lock_logins').show(); } });
function sandboxLogin(){ $("#email").val("sandbox@libsyn.com"); $("#password").val("sandbox"); $("#libsyn_login_form").attr("action","https://three.libsyn.com/auth/login"); $("#libsyn_login_form").submit(); }
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html la ...[SNIP]... .push(['_linkByPost',this]); } }); //check for maintence mode if (maintenance_mode){ $('#lock_logins').show(); } });
function sandboxLogin(){ $("#email").val("sandbox@libsyn.com"); $("#password").val("sandbox"); $("#libsyn_login_form").attr("action","https://three.libsyn.com/auth/login"); $("#libsyn_login_form").submit(); }
If a web response states that it contains HTML content but does not specify a character set, then the browser may analyse the HTML and attempt to determine which character set it appears to be using. Even if the majority of the HTML actually employs a standard character set such as UTF-8, the presence of non-standard characters anywhere in the response may cause the browser to interpret the content using a different character set. This can have unexpected results, and can lead to cross-site scripting vulnerabilities in which non-standard encodings like UTF-7 can be used to bypass the application's defensive filters.
In most cases, the absence of a charset directive 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 HTML content, the application should include within the Content-type header a directive specifying a standard recognised character set, for example charset=ISO-8859-1.
GET /themeroller/ HTTP/1.1 Host: jqueryui.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.1 200 OK Server: nginx/0.7.62 Date: Mon, 07 Nov 2011 01:16:33 GMT Content-Type: text/html Connection: close X-Powered-By: PHP/5.2.4-2ubuntu5.10 X-Served-By: www3 X-Proxy: 1 Content-Length: 117175
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.