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46 Web Application Penetration Testing Sample output is presented on a screenshot below: Wapplyzer is a Firefox Chrome plug-in. It works only on regular expression matching and doesn’t need anything other than the page to be loaded on browser. It works completely at the browser level and gives results in the form of icons. Although sometimes it has false positives, this is very handy to have notion of what technologies were used to construct a target website immediately after browsing a page. Sample output of a plug-in is presented on a screenshot below. BlindElephant Website: https:/community.qualys.com/community/blindelephant This great tool works on the principle of static file checksum based version difference thus providing a very high quality of fingerprinting. Language: Python Sample output of a successful fingerprint: pentester$ python BlindElephant.py http:/my_target drupal Loaded /Library/Python/2.7/site-packages/blindelephant/ dbs/drupal.pkl with 145 versions, 478 differentiating paths, and 434 version groups. Starting BlindElephant fingerprint for version of drupal at http:/ my_target Hit http:/my_target/CHANGELOG.txt File produced no match. Error: Retrieved file doesn’t match known fingerprint. 527b085a3717bd691d47713dff74acf4 Hit http:/my_target/INSTALL.txt File produced no match. Error: Retrieved file doesn’t match known fingerprint. 14dfc133e4101be6f0ef5c64566da4a4 Hit http:/my_target/misc/drupal.js Possible versions based on result: 7.12, 7.13, 7.14 Hit http:/my_target/MAINTAINERS.txt File produced no match. Error: Retrieved file doesn’t match known fingerprint. 36b740941a19912f3fdbfcca7caa08ca Hit http:/my_target/themes/garland/style.css Possible versions based on result: 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 7.10, 7.11, 7.12, 7.13, 7.14 ... Fingerprinting resulted in: 7.14 Best Guess: 7.14 Wappalyzer Website: http:/wappalyzer.com References Whitepapers • Saumil Shah: “An Introduction to HTTP fingerprinting” - http:/www. net-square.com/httprint_paper.html • Anant Shrivastava : “Web Application Finger Printing” - http:/anantshri.info/articles/web_app_finger_printing.html Remediation The general advice is to use several of the tools described above and check logs to better understand what exactly helps an attacker to disclose the web framework. By performing multiple scans after changes have been made to hide framework tracks, it’s possible to achieve a better level of security and to make sure of the framework can not be detected by automatic scans. Below are some specific recommendations by framework marker location and some additional interesting approaches. HTTP headers Check the configuration and disable or obfuscate all HTTP-headers that disclose information the technologies used. Here is an interesting article about HTTP-headers obfuscation using Netscaler: http:/ grahamhosking.blogspot.ru/2013/07/obfuscating-http-header-using-netscaler.html Cookies It is recommended to change cookie names by making changes in the corresponding configuration files. HTML source code Manually check the contents of the HTML code and remove everything that explicitly points to the framework. General guidelines: • Make sure there are no visual markers disclosing the framework • Remove any unnecessary comments (copyrights, bug information, specific framework comments) • Remove META and generator tags • Use the companies own css or js files and do not store those in a
47 Web Application Penetration Testing framework-specific folders • Do not use default scripts on the page or obfuscate them if they must be used. Specific files and folders General guidelines: • Remove any unnecessary or unused files on the server. This implies text files disclosing information about versions and installation too. • Restrict access to other files in order to achieve 404-response when accessing them from outside. This can be done, for example, by modifying htaccess file and adding RewriteCond or RewriteRule there. An example of such restriction for two common WordPress folders is presented below. RewriteCond %{REQUEST_URI} /wp-login\.php$ [OR] RewriteCond %{REQUEST_URI} /wp-admin/$ RewriteRule $ /http:/your_website [R=404,L] However, these are not the only ways to restrict access. In order to automate this process, certain framework-specific plugins exist. One example for WordPress is StealthLogin (http:/wordpress.org/plugins/ stealth-login-page). Additional approaches General guidelines: [1] Checksum management The purpose of this approach is to beat checksum-based scanners and not let them disclose files by their hashes. Generally, there are two approaches in checksum management: • Change the location of where those files are placed (i.e. move them to another folder, or rename the existing folder) • Modify the contents - even slight modification results in a completely different hash sum, so adding a single byte in the end of the file should not be a big problem. [2] Controlled chaos A funny and effective method that involves adding bogus files and folders from other frameworks in order to fool scanners and confuse an attacker. But be careful not to overwrite existing files and folders and to break the current framework! Map Application Architecture (OTG-INFO-010) Summary The complexity of interconnected and heterogeneous web server infrastructure can include hundreds of web applications and makes configuration management and review a fundamental step in testing and deploying every single application. In fact it takes only a single vulnerability to undermine the security of the entire infrastructure, and even small and seemingly unimportant problems may evolve into severe risks for another application on the same server. To address these problems, it is of utmost importance to perform an in-depth review of configuration and known security issues. Before performing an in-depth review it is necessary to map the network and application architecture. The different elements that make up the infrastructure need to be determined to understand how they interact with a web application and how they affect security. How to Test Map the application architecture The application architecture needs to be mapped through some test to determine what different components are used to build the web application. In small setups, such as a simple CGI-based application, a single server might be used that runs the web server which executes the C, Perl, or Shell CGIs application, and perhaps also the authentication mechanism. On more complex setups, such as an online bank system, multiple servers might be involved. These may include a reverse proxy, a frontend web server, an application server and a database server or LDAP server. Each of these servers will be used for different purposes and might be even be divided in different networks with firewalls between them. This creates different DMZs so that access to the web server will not grant a remote user access to the authentication mechanism itself, and so that compromises of the different elements of the architecture can be isolated so that they will not compromise the whole architecture. Getting knowledge of the application architecture can be easy if this information is provided to the testing team by the application developers in document form or through interviews, but can also prove to be very difficult if doing a blind penetration test. In the latter case, a tester will first start with the assumption that there is a simple setup (a single server). Then they will retrieve information from other tests and derive the different elements, question this assumption and extend the architecture map. The tester will start by asking simple questions such as: “Is there a firewalling system protecting the web server?”. This question will be answered based on the results of network scans targeted at the web server and the analysis of whether the network ports of the web server are being filtered in the network edge (no answer or ICMP unreachables are received) or if the server is directly connected to the Internet (i.e. returns RST packets for all non-listening ports). This analysis can be enhanced to determine the type of firewall used based on network packet tests. Is it a stateful firewall or is it an access list filter on a router? How is it configured? Can it be bypassed? Detecting a reverse proxy in front of the web server needs to be done by the analysis of the web server banner, which might directly disclose the existence of a reverse proxy (for example, if ‘WebSEAL’[1] is returned). It can also be determined by obtaining the answers given by the web server to requests and comparing them to the expected answers. For example, some reverse proxies act as “intrusion prevention systems” (or web-shields) by blocking known attacks targeted at the web server. If the web server is known to answer with a 404 message to a request that targets an unavailable page and returns a different error message for some common web attacks like those done by CGI scanners, it might be an indication of a reverse proxy (or an application-level firewall) which is filtering the requests and returning a different error page than the one expected. Another example: if the web server returns a set of available HTTP methods (including TRACE) but the expected methods return errors then there is probably something in between blocking them. In some cases, even the protection system gives itself away: GET /web-console/ServerInfo.jsp%00 HTTP/1.0 HTTP/1.0 200 Pragma: no-cache
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