Testing for SSI Injection (OTG-INPVAL-009) - Revision history

Andrew Muller: Andrew Muller moved page Testing for SSI Injection (OTG-INPVAL-010) to Testing for SSI Injection (OTG-INPVAL-009)

2014-08-08T12:03:55Z

Andrew Muller moved page Testing for SSI Injection (OTG-INPVAL-010) to Testing for SSI Injection (OTG-INPVAL-009)

Andrew Muller at 16:14, 31 July 2014

2014-07-31T16:14:31Z

Andrew Muller: Andrew Muller moved page Testing for SSI Injection (OWASP-DV-009) to Testing for SSI Injection (OTG-INPVAL-010): Align with Common Numbering

2014-07-31T14:35:21Z

Andrew Muller moved page Testing for SSI Injection (OWASP-DV-009) to Testing for SSI Injection (OTG-INPVAL-010): Align with Common Numbering

Jane O'Connor at 10:03, 19 May 2014

2014-05-19T10:03:06Z

Jane O'Connor: Final edit

2014-05-19T10:02:24Z

Final edit

Shady: References

2013-05-12T13:04:47Z

References

Chris Andre Dale: The ls command does not necessarily list a file, but it definitely provide a directory listing.

2013-03-01T08:26:51Z

The ls command does not necessarily list a file, but it definitely provide a directory listing.

Mmeucci at 14:52, 9 October 2012

2012-10-09T14:52:15Z

KirstenS: /* References */

2009-02-09T13:17:51Z

‎References

KirstenS: /* Gray Box testing and example */

2009-02-09T13:16:59Z

‎Gray Box testing and example

@@ Line 2: / Line 2: @@
-== Brief Summary ==
+== Summary ==
 Web servers usually give developers the ability to add small pieces of dynamic code inside static HTML pages, without having to deal with full-fledged server-side or client-side languages. This feature is incarnated by the '''[[Server-Side Includes %28SSI%29 Injection|Server-Side Includes]]''' ('''SSI'''). In SSI injection testing, we test if it is possible to inject into the application data that will be interpreted by SSI mechanisms. A successful exploitation of this vulnerability allows an attacker to inject code into HTML pages or even perform remote code execution.
 Server-Side Includes are directives that the web server parses before serving the page to the user. They represent an alternative to writing CGI programs or embedding code using server-side scripting languages, when there's only need to perform very simple tasks. Common SSI implementations provide commands to include external files, to set and print web server CGI environment variables, and to execute external CGI scripts or system commands.
@@ Line 47: / Line 45: @@
 This is a vulnerability very similar to a classical scripting language injection vulnerability. One mitigation is that the web server needs to be configured to allow SSI. On the other hand, SSI injection vulnerabilities are often simpler to exploit, since SSI directives are easy to understand and, at the same time, quite powerful, e.g., they can output the content of files and execute system commands.<br>
-== Black Box testing ==
+=== Black Box testing ===
 The first thing to do when testing in a Black Box fashion is finding if the web server actually supports SSI directives. Often, the answer is yes, as SSI support is quite common. To find out we just need to discover which kind of web server is running on our target, using classic information gathering techniques.<br>
@@ Line 93: / Line 92: @@
-== Gray Box testing and example ==
+=== Gray Box testing ===
 If we have access to the application source code, we can quite easily find out:<br>
@@ Line 103: / Line 102: @@
 Performing these steps is mostly a matter of using grep to find the right keywords inside the source code (SSI directives, CGI environment variables, variables assignment involving user input, filtering functions and so on).
 == References ==
@@ Line 112: / Line 117: @@
 * SSI Injection instead of JavaScript Malware - http://jeremiahgrossman.blogspot.com/2006/08/ssi-injection-instead-of-javascript.html
 * IIS: "Notes on Server-Side Includes (SSI) syntax" - http://blogs.iis.net/robert_mcmurray/archive/2010/12/28/iis-notes-on-server-side-includes-ssi-syntax-kb-203064-revisited.aspx<br>

@@ Line 118: / Line 118: @@
 * Paros - http://www.parosproxy.org/index.shtml
 * [[OWASP WebScarab Project|WebScarab]]
-* String searcher: grep - http://www.gnu.org/software/grep, your favorite text editor
+* String searcher: grep - http://www.gnu.org/software/grep

@@ Line 5: / Line 5: @@
 Web servers usually give developers the ability to add small pieces of dynamic code inside static HTML pages, without having to deal with full-fledged server-side or client-side languages. This feature is incarnated by the '''[[Server-Side Includes %28SSI%29 Injection|Server-Side Includes]]''' ('''SSI'''). In SSI injection testing, we test if it is possible to inject into the application data that will be interpreted by SSI mechanisms. A successful exploitation of this vulnerability allows an attacker to inject code into HTML pages or even perform remote code execution.
 == Description of the Issue ==
-Server-Side Includes are directives that the web server parses before serving the page to the user. They represent an alternative to writing CGI programs or embedding code using server-side scripting languages, when there's only need to perform very simple tasks. Common SSI implementations provide commands to include external files, to set and print web server CGI environment variables, and to execute external CGI scripts or system commands.<br>
+Server-Side Includes are directives that the web server parses before serving the page to the user. They represent an alternative to writing CGI programs or embedding code using server-side scripting languages, when there's only need to perform very simple tasks. Common SSI implementations provide commands to include external files, to set and print web server CGI environment variables, and to execute external CGI scripts or system commands.
 Putting an SSI directive into a static HTML document is as easy as writing a piece of code like the following:<br>
@@ Line 35: / Line 37: @@
 to include the output of a system command.<br>
 Then, if the web server's SSI support is enabled, the server will parse these directives. In the default configuration, usually, most web servers don't allow the use of the '''''exec''''' directive to execute system commands.<br>
 As in every bad input validation situation, problems arise when the user of a web application is allowed to provide data that makes the application or the web server behave in an unforeseen manner. With regard to SSI injection, the attacker could provide input that, if inserted by the application (or maybe directly by the server) into a dynamically generated page, would be parsed as one or more SSI directives.<br>
 This is a vulnerability very similar to a classical scripting language injection vulnerability. One mitigation is that the web server needs to be configured to allow SSI. On the other hand, SSI injection vulnerabilities are often simpler to exploit, since SSI directives are easy to understand and, at the same time, quite powerful, e.g., they can output the content of files and execute system commands.<br>
 == Black Box testing ==
 The first thing to do when testing in a Black Box fashion is finding if the web server actually supports SSI directives. Often, the answer is yes, as SSI support is quite common. To find out we just need to discover which kind of web server is running on our target, using classic information gathering techniques.<br>
 Whether we succeed or not in discovering this piece of information, we could guess if SSI are supported just by looking at the content of the target web site. If it contains '''''.shtml''''' files, then SSI are probably supported, as this extension is used to identify pages containing these directives. Unfortunately, the use of the '''''shtml''''' extension is not mandatory, so not having found any '''''shtml''''' files doesn't necessarily mean that the target is not prone to SSI injection attacks.<br>
 The next step consists of determining if an SSI injection attack is actually possible and, if so, what are the input points that we can use to inject our malicious code.<br>
 The testing activity required to do this is exactly the same used to test for other code injection vulnerabilities. In particular, we need to find every page where the user is allowed to submit some kind of input, and verify whether the application is correctly validating the submitted input. If sanitization is insufficient, we need to test if we can provide data that is going to be displayed unmodified (for example, in an error message or forum post). Besides common user-supplied data, input vectors that should always be considered are HTTP request headers and cookies content, since they can be easily forged.<br>
 Once we have a list of potential injection points, we can check if the input is correctly validated and then find out where the provided input is stored. We need to make sure that we can inject characters used in SSI directives:<br>
@@ Line 68: / Line 79: @@
 <script>alert("XSS")</script>
 </pre>
 If the application is vulnerable, the directive is injected and it would be interpreted by the server the next time the page is served, thus including the content of the Unix standard password file.<br>
 The injection can be performed also in HTTP headers, if the web application is going to use that data to build a dynamically generated page:<br>
@@ Line 78: / Line 91: @@
 User-Agent: <!--#include virtual="/proc/version"-->
 </pre>
 == Gray Box testing and example ==
@@ Line 85: / Line 99: @@
 # Where user input, cookie content and HTTP headers are handled. The complete list of input vectors is then quickly determined.<br>
 # How the input is handled, what kind of filtering is performed, what characters the application is not letting through, and how many types of encoding are taken into account.<br>
 Performing these steps is mostly a matter of using grep to find the right keywords inside the source code (SSI directives, CGI environment variables, variables assignment involving user input, filtering functions and so on).
 == References ==
@@ Line 96: / Line 112: @@
 * SSI Injection instead of JavaScript Malware - http://jeremiahgrossman.blogspot.com/2006/08/ssi-injection-instead-of-javascript.html
 * IIS: "Notes on Server-Side Includes (SSI) syntax" - http://blogs.iis.net/robert_mcmurray/archive/2010/12/28/iis-notes-on-server-side-includes-ssi-syntax-kb-203064-revisited.aspx<br>
 '''Tools'''<br>

@@ Line 95: / Line 95: @@
 * Header Based Exploitation - http://www.cgisecurity.net/papers/header-based-exploitation.txt<br>
 * SSI Injection instead of JavaScript Malware - http://jeremiahgrossman.blogspot.com/2006/08/ssi-injection-instead-of-javascript.html
 '''Tools'''<br>
@@ Line 101: / Line 102: @@
 * [[OWASP WebScarab Project|WebScarab]]
 * String searcher: grep - http://www.gnu.org/software/grep, your favorite text editor

@@ Line 28: / Line 28: @@
 </pre>
-to include the content of a file.<br>
+to include the content of a file or list files in a directory.<br>
 <pre>

← Older revision	Revision as of 12:03, 8 August 2014
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← Older revision	Revision as of 14:35, 31 July 2014
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← Older revision		Revision as of 14:52, 9 October 2012
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 == References ==
 '''Whitepapers'''<br>
 * Apache Tutorial: "Introduction to Server Side Includes" - http://httpd.apache.org/docs/1.3/howto/ssi.html<br>
 * Apache: "Module mod_include" - http://httpd.apache.org/docs/1.3/mod/mod_include.html<br>
@@ Line 102: / Line 101: @@
 * [[OWASP WebScarab Project|WebScarab]]
 * String searcher: grep - http://www.gnu.org/software/grep, your favorite text editor