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 defences:
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.
1.1. http://hotfile.com/ [name of an arbitrarily supplied request parameter]next
Summary
Severity:
High
Confidence:
Certain
Host:
http://hotfile.com
Path:
/
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 4c86d"><script>alert(1)</script>d4770aceb91 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 /?4c86d"><script>alert(1)</script>d4770aceb91=1 HTTP/1.1 Host: hotfile.com Proxy-Connection: keep-alive User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.112 Safari/535.1 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 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
Response
HTTP/1.1 200 OK Cache-Control: no-cache, must-revalidate Expires: Sat, 26 Jul 1997 05:00:00 GMT Content-type: text/html Connection: close Date: Wed, 17 Aug 2011 01:07:25 GMT Server: lighttpd/1.4.26 Content-Length: 19901
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head>
1.2. http://hotfile.com/affiliate.html [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://hotfile.com
Path:
/affiliate.html
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 35782"><script>alert(1)</script>44acc2cf687 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.
1.3. http://hotfile.com/forgotpassword.html [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://hotfile.com
Path:
/forgotpassword.html
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 264bb"><script>alert(1)</script>0ff3481a3bf 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.
1.4. http://hotfile.com/news.html [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://hotfile.com
Path:
/news.html
Issue detail
The name of an arbitrarily supplied request parameter is copied into the value of an HTML tag attribute which is not encapsulated in any quotation marks. The payload 38030><script>alert(1)</script>8782e258893 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.
1.5. http://hotfile.com/news.html [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://hotfile.com
Path:
/news.html
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 81483"><script>alert(1)</script>4101186456b 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.
1.6. http://hotfile.com/premium.html [name of an arbitrarily supplied request parameter]previousnext
Summary
Severity:
High
Confidence:
Certain
Host:
http://hotfile.com
Path:
/premium.html
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 33061"><script>alert(1)</script>367e4a9df44 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.
The application publishes a Flash cross-domain policy which allows access from any domain.
Allowing access from all domains means that any domain can perform two-way interaction with this application. Unless the application consists entirely of unprotected public content, this policy is likely to present a significant security risk.
Issue background
The Flash cross-domain policy controls whether Flash client components running on other domains can perform two-way interaction with the domain which publishes the policy. If another domain is allowed by the policy, then that domain can potentially attack users of the application. If a user is logged in to the application, and visits a domain allowed by the policy, then any malicious content running on that domain can potentially gain full access to the application within the security context of the logged in user.
Even if an allowed domain is not overtly malicious in itself, security vulnerabilities within that domain could potentially be leveraged by a third-party attacker to exploit the trust relationship and attack the application which allows access.
Issue remediation
You should review the domains which are allowed by the Flash cross-domain policy and determine whether it is appropriate for the application to fully trust both the intentions and security posture of those domains.
Request
GET /crossdomain.xml HTTP/1.0 Host: hotfile.com
Response
HTTP/1.0 200 OK Content-Type: text/xml Accept-Ranges: bytes ETag: "403596772" Last-Modified: Tue, 24 May 2011 11:54:45 GMT Content-Length: 223 Connection: close Date: Wed, 17 Aug 2011 01:07:21 GMT Server: lighttpd/1.4.26
Passwords submitted over an unencrypted connection are vulnerable to capture by an attacker who is suitably positioned on the network. This includes any malicious party located on the user's own network, within their ISP, within the ISP used by the application, and within the application's hosting infrastructure. Even if switched networks are employed at some of these locations, techniques exist to circumvent this defence and monitor the traffic passing through switches.
Issue remediation
The application should use transport-level encryption (SSL or TLS) to protect all sensitive communications passing between the client and the server. Communications that should be protected include the login mechanism and related functionality, and any functions where sensitive data can be accessed or privileged actions can be performed. These areas of the application should employ their own session handling mechanism, and the session tokens used should never be transmitted over unencrypted communications. If HTTP cookies are used for transmitting session tokens, then the secure flag should be set to prevent transmission over clear-text HTTP.
Most browsers have a facility to remember user credentials that are entered into HTML forms. This function can be configured by the user and also by applications which employ user credentials. If the function is enabled, then credentials entered by the user are stored on their local computer and retrieved by the browser on future visits to the same application.
The stored credentials can be captured by an attacker who gains access to the computer, either locally or through some remote compromise. Further, methods have existed whereby a malicious web site can retrieve the stored credentials for other applications, by exploiting browser vulnerabilities or through application-level cross-domain attacks.
Issue remediation
To prevent browsers from storing credentials entered into HTML forms, you should include the attribute autocomplete="off" within the FORM tag (to protect all form fields) or within the relevant INPUT tags (to protect specific individual fields).
The POSTing of data between domains does not necessarily constitute a security vulnerability. You should review the contents of the information that is being transmitted between domains, and determine whether the originating application should be trusting the receiving domain with this information.
Note that Burp has not identified any specific security vulnerabilities with this functionality, and you should manually review it to determine whether any problems exist.
Issue background
File upload functionality is commonly associated with a number of vulnerabilities, including:
File path traversal
Persistent cross-site scripting
Placing of other client-executable code into the domain
Transmission of viruses and other malware
Denial of service
You should review the file upload functionality to understand its purpose, and establish whether uploaded content is ever returned to other application users, either through their normal usage of the application or by being fed a specific link by an attacker.
Some factors to consider when evaluating the security impact of this functionality include:
Whether uploaded content can subsequently be downloaded via a URL within the application.
What Content-type and Content-disposition headers the application returns when the file's content is downloaded.
Whether it is possible to place executable HTML/JavaScript into the file, which executes when the file's contents are viewed.
Whether the application performs any filtering on the file extension or MIME type of the uploaded file.
Whether it is possible to construct a hybrid file containing both executable and non-executable content, to bypass any content filters - for example, a file containing both a GIF image and a Java archive (known as a GIFAR file).
What location is used to store uploaded content, and whether it is possible to supply a crafted filename to escape from this location.
Whether archive formats such as ZIP are unpacked by the application.
How the application handles attempts to upload very large files, or decompression bomb files.
Issue remediation
File upload functionality is not straightforward to implement securely. Some recommendations to consider in the design of this functionality include:
Use a server-generated filename if storing uploaded files on disk.
Inspect the content of uploaded files, and enforce a whitelist of accepted, non-executable content types. Additionally, enforce a blacklist of common executable formats, to hinder hybrid file attacks.
Enforce a whitelist of accepted, non-executable file extensions.
If uploaded files are downloaded by users, supply an accurate non-generic Content-type header, and also a Content-disposition header which specifies that browsers should handle the file as an attachment.
Enforce a size limit on uploaded files (for defence-in-depth, this can be implemented both within application code and in the web server's configuration.
Reject attempts to upload archive formats such as ZIP.
Request
GET / HTTP/1.1 Host: hotfile.com Proxy-Connection: keep-alive User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.1 (KHTML, like Gecko) Chrome/13.0.782.112 Safari/535.1 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 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
Response
HTTP/1.1 200 OK Cache-Control: no-cache, must-revalidate Expires: Sat, 26 Jul 1997 05:00:00 GMT Content-type: text/html Connection: close Date: Wed, 17 Aug 2011 01:07:20 GMT Server: lighttpd/1.4.26 Content-Length: 19073
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head>
