4.0

More documents

Recommendations

Info

188 Web Application Penetration Testing • Test Upload of Unexpected File Types (OTG-BUSLOGIC-008) Tools • Metasploit’s payload generation functionality • Intercepting proxy References • OWASP - Unrestricted File Upload - https://www.owasp.org index.php/Unrestricted_File_Upload • Why File Upload Forms are a Major Security Threat - http:/ www.acunetix.com/websitesecurity/upload-forms-threat/ • File upload security best practices: Block a malicious file upload http://www.computerweekly.com/answer/File-uploadsecurity-best-practices-Block-a-malicious-file-upload • Overview of Malicious File Upload Attacks http:/securitymecca.com/article/overview-of-malicious-fileupload-attacks/ • Stop people uploading malicious PHP files via forms http://stackoverflow.com/questions/602539/stop-peopleuploading-malicious-php-files-via-forms • How to Tell if a File is Malicious http://www.techsupportalert.com/content/how-tell-if-filemalicious.htm • CWE-434: Unrestricted Upload of File with Dangerous Type http://cwe.mitre.org/data/definitions/434.html • Implementing Secure File Upload http://infosecauditor.wordpress.com/tag/malicious-fileupload/ • Watchful File Upload http://palizine.plynt.com/issues/2011Apr/file-upload/ • Matasploit Generating Payloads http://www.offensive-security.com/metasploit-unleashed/ Generating_Payloads • Project Shellcode – Shellcode Tutorial 9: Generating Shellcode Using Metasploit http://www.projectshellcode. com/?q=node/29 • Anti-Malware Test file - http://www.eicar.org/86-0-Intended use.html Remediation While safeguards such as black or white listing of file extensions, using “Content-Type” from the header, or using a file type recognizer may not always be protections against this type of vulnerability. Every application that accepts files from users must have a mechanism to verify that the uploaded file does not contain malicious code. Uploaded files should never be stored where the users or attackers can directly access them. Client-Side Testing Client-Side testing is concerned with the execution of code on the client, typically natively within a web browser or browser plugin. The execution of code on the client-side is distinct from executing on the server and returning the subsequent content. Testing for DOM-based Cross site scripting (OTG-CLIENT-001) Summary DOM-based Cross-Site Scripting is the de-facto name for XSS bugs which are the result of active browser-side content on a page, typically JavaScript, obtaining user input and then doing something unsafe with it which leads to execution of injected code. This document only discusses JavaScript bugs which lead to XSS. The DOM, or Document Object Model, is the structural format used to represent documents in a browser. The DOM enables dynamic scripts such as JavaScript to reference components of the document such as a form field or a session cookie. The DOM is also used by the browser for security - for example to limit scripts on different domains from obtaining session cookies for other domains. A DOM-based XSS vulnerability may occur when active content, such as a JavaScript function, is modified by a specially crafted request such that a DOM element that can be controlled by an attacker. There have been very few papers published on this topic and, as such, very little standardization of its meaning and formalized testing exists. How to Test Not all XSS bugs require the attacker to control the content returned from the server, but can instead abuse poor JavaScript coding practices to achieve the same results. The consequences are the same as a typical XSS flaw, only the means of delivery is different. In comparison to other cross site scripting vulnerabilities (reflected and stored XSS), where an unsanitized parameter is passed by the server, returned to the user and executed in the context of the user’s browser, a DOM-based XSS vulnerability controls the flow of the code by using elements of the Document Object Model (DOM) along with code crafted by the attacker to change the flow. Due to their nature, DOM-based XSS vulnerabilities can be executed in many instances without the server being able to determine what is actually being executed. This may make many of the general XSS filtering and detection techniques impotent to such attacks. The first hypothetical example uses the following client side code: An attacker may append #alert(‘xss’) to the affected page URL which would, when executed, display the alert box. In this instance, the appended code would not be sent to the server as everything after the # character is not treated as part of the query by the browser but as a fragment. In this example, the code is immediately executed and an alert of “xss” is displayed by the page. Unlike the more common types of cross
189 Web Application Penetration Testing site scripting (Stored and Reflected) in which the code is sent to the server and then back to the browser, this is executed directly in the user’s browser without server contact. The consequences of DOM-based XSS flaws are as wide ranging as those seen in more well known forms of XSS, including cookie retrieval, further malicious script injection, etc. and should therefore be treated with the same severity. Black Box testing Blackbox testing for DOM-Based XSS is not usually performed since access to the source code is always available as it needs to be sent to the client to be executed. Gray Box testing Testing for DOM-Based XSS vulnerabilities: JavaScript applications differ significantly from other types of applications because they are often dynamically generated by the server, and to understand what code is being executed, the website being tested needs to be crawled to determine all the instances of JavaScript being executed and where user input is accepted. Many websites rely on large libraries of functions, which often stretch into the hundreds of thousands of lines of code and have not been developed in-house. In these cases, top-down testing often becomes the only really viable option, since many bottom level functions are never used, and analyzing them to determine which are sinks will use up more time than is often available. The same can also be said for top-down testing if the inputs or lack thereof is not identified to begin with. User input comes in two main forms: • Input written to the page by the server in a way that does not allow direct XSS • Input obtained from client-side JavaScript objects Here are two examples of how the server may insert data into JavaScript: And here are two examples of input from client-side JavaScript objects: While there is little difference to the JavaScript code in how they are retrieved, it is important to note that when input is received via the server, the server can apply any permutations to the data that it desires, whereas the permutations performed by JavaScript objects are fairly well understood and documented, and so if someFunction in the above example were a sink, then the exploitability of the former would depend on the filtering done by the server, whereas the latter would depend on the encoding done by the browser on the window.referer object. Stefano Di Paulo has written an excellent article on what browsers return when asked for the various elements of a URL using the document. and location. attributes. Additionally, JavaScript is often executed outside of blocks, as evidenced by the many vectors which have led to XSS filter bypasses in the past, and so, when crawling the application, it is important to note the use of scripts in places such as event handlers and CSS blocks with expression attributes. Also, note that any off-site CSS or script objects will need to be assessed to determine what code is being executed. Automated testing has only very limited success at identifying and validating DOM-based XSS as it usually identifies XSS by sending a specific payload and attempts to observe it in the server response. This may work fine for the simple example provided below, where the message parameter is reflected back to the user: but may not be detected in the following contrived case: For this reason, automated testing will not detect areas that may be susceptible to DOM-based XSS unless the testing tool can perform addition analysis of the client side code. Manual testing should therefore be undertaken and can be done by examining areas in the code where parameters are referred to that may be useful to an attacker. Examples of such areas include places where code is dynamically written to the page and elsewhere where the DOM is modified or even where scripts are directly executed. Further examples are described in the excellent DOM XSS article by Amit Klein, referenced at the end of this section. References OWASP Resources • DOM based XSS Prevention Cheat Sheet Whitepapers • Document Object Model (DOM) - http://en.wikipedia.org/wiki Document_Object_Model • DOM Based Cross Site Scripting or XSS of the Third Kind - Amit Klein: http://www.webappsec.org/projects/articles/071105. shtml • Browser location/document URI/URL Sources - https://code google.com/p/domxsswiki/wiki/LocationSources • i.e., what is returned when the user asks the browser for things like document.URL, document.baseURI, location, location.href, etc. Testing for JavaScript Execution (OTG-CLIENT-002) Summary A JavaScript Injection vulnerability is a subtype of Cross Site Scripting (XSS) that involves the ability to inject arbitrary JavaScript code that is executed by the application inside the victim’s browser. This vulnerability can have many consequences, like disclosure of a user’s session cookies that could be used to impersonate the victim, or, more generally, it can allow the attacker to modify the page content seen by the victims or the application behavior. How to Test Such vulnerability occurs when the application lacks of a proper user supplied input and output validation. JavaScript is used to dynamically populate web pages, this injection occur during this content processing phase and consequently affect the victim. When trying to exploit this kind of issues, consider that some characters are treated differently by different browsers. For reference see the DOM XSS Wiki. The following script does not perform any validation of the vari-
Page 1 and 2:
1 Testing Guide 4.0 Project Leaders
Page 3 and 4:
Testing Guide Foreword - Table of c
Page 5 and 6:
3 Testing Guide Foreword - Table of
Page 7 and 8:
5 Testing Guide Foreword - By Eoin
Page 9 and 10:
7 Testing Guide Frontispiece 1 Test
Page 11 and 12:
9 Testing Guide Introduction 2 The
Page 13 and 14:
11 Testing Guide Introduction vide
Page 15 and 16:
13 Testing Guide Introduction Testi
Page 17 and 18:
15 Testing Guide Introduction laid
Page 19 and 20:
17 Testing Guide Introduction valid
Page 21 and 22:
19 Testing Guide Introduction USER
Page 23 and 24:
21 Testing Guide Introduction ment
Page 25 and 26:
23 Testing Guide Introduction offen
Page 27 and 28:
25 The OWASP Testing Framework sect
Page 29 and 30:
27 Web Application Penetration Test
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51 and 52:
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
101 Web Application Penetration Tes
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140: 137 Web Application Penetration Tes
Page 189: 187 Web Application Penetration Tes
Page 211 and 212: 209 same code can be applied to ses
Page 213 and 214: 211 Reporting Test ID Lowest versio
Page 215 and 216: 213 Reporting Test ID Business Logi
Page 217 and 218: 215 Appendix kajfghlhfkcocafkcjlajl
Page 219 and 220: 217 Appendix Testing - http:/www.ni
Page 221 and 222: 219 Cross Site Scripting (XSS) For
Page 223 and 224: 221 LDAP Injection For details on L
show all

4.0

Create successful ePaper yourself

Delete template?

Save as template?