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advanced-use-cases.rst

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Advanced use cases

Complex Web applications

Some Web applications use browser-side technologies such as JavaScript, Flash and Java applets, technologies that the browsers understand; and w3af is still unable to.

A plugin called spider_man was created to solve this issue, allowing users to analyze complex Web applications. The plugin starts an HTTP proxy which is used by the user to navigate the target site, during this process the plugin will extract information from the requests and send them to the enabled audit plugins.

Note

The spider_man plugin can be used when Javascript, Flash, Java applets or any other browser side technology is present. The only requirement is for the user to manually browse the site using spider_man as HTTP(s) proxy.

Note

See :doc:`ca-config` for details about how to configure w3af's certificate authority (CA) in your browser.

A simple example will clarify things, let's suppose that w3af is auditing a site and can't find any links on the main page. After a closer inspection of the results by the user, it is clear that the main page has a Java applet menu where all the other sections are linked from. The user runs w3af once again and now activates the crawl.spider_man plugin, navigates the site manually using the browser and the spiderman proxy. When the user has finished his browsing, w3af will continue with all the hard auditing work.

This is a sample spider_man plugin run:

w3af>>> plugins
w3af/plugins>>> crawl spider_man
w3af/plugins>>> audit sqli
w3af/plugins>>> back
w3af>>> target
w3af/target>>> set target http://localhost/
w3af/target>>> back
w3af>>> start
spider_man proxy is running on 127.0.0.1:44444 .
Please configure your browser to use these proxy settings and navigate the target site.
To exit spider_man plugin please navigate to http://127.7.7.7/spider_man?terminate .

Now the user configures his browser to use the 127.0.0.1:44444 address as HTTP proxy and navigates the target site, when he finishes navigating the site sections he wants to audit he navigates to http://127.7.7.7/spider_man?terminate which will stop the proxy and finish the plugin. The audit.sqli plugin will run over the identified HTTP requests.

Ignoring specific forms

w3af allows users to configure which forms to ignore using a feature called form ID exclusions. This feature was created when users identified limitations in the previous (more simplistic) exclusion model which only allowed forms to be ignored using URL matching.

Exclusions are configured using a list of form IDs provided in the following format:

[{"action":"/products/.*",
  "inputs": ["comment"],
  "attributes": {"class": "comments-form"},
  "hosted_at_url": "/products/.*",
  "method": "get"}]

Where:

  • action is a regular expression matching the URL path of the form action,
  • inputs is a list containing the form inputs,
  • attributes is a map containing the <form> tag attributes,
  • hosted-at-url is a regular expression matching the URL path where the form was found,
  • method is the HTTP method using to submit the form.

So, for example, if a user wants to ignore all forms which are sent using the HTTP POST method he would configure the following form ID:

[{"method": "post"}]

If the user decides to ignore all forms which are sent to a specific action and contain the class attribute with value comments-form he would configure:

[{"action":"/products/comments",
  "attributes": {"class": "comments-form"}}]

More than one form ID can be specified in the list, for example the following will exclude all forms with methods POST and PUT:

[{"method": "post"}, {"method": "put"}]

Ignoring all forms is also possible using:

[{}]

This feature is configured using two variables in the misc-settings menu:

  • form_id_list: A string containing the format explained above to match forms.
  • form_id_action: The default action is to exclude the forms which are found by w3af and match at least one of the form IDs specified in form_id_list, but the user can also specify include to only scan the forms which match at least one of the form IDs in the list.

To ease the configuration of this setting w3af will add a debug line to the output (make sure to set verbose to true to see these lines in the output file plugin) containing the form ID of each identified form.

Note

This feature works well together with blacklist_http_request. w3af will only send requests to the target if they match both filters.

Ignoring URLs during fuzzing

w3af allows users to configure a set of URLs that will be used for crawling (finding new URLs) but will be ignored during the audit phase. In order to use this feature users need to set the URLs to be excluded in misc-settings.blacklist_audit.

Variants

Crawling web applications is a challenging task: some web applications have thousands of URLs, some of those with one or more HTML forms. Let's explore a common e-commerce site which has one thousand products, each shown in a different URL such as:

  • /products/title-product-A
  • /products/another-product-title
  • /review-comment?id=6631

When browsing to each of those URLs the HTML contains three forms, one to add the product to the cart, another one to favorite the product and finally one to ask a question regarding this product. The form action for each form is set to the product page.

The main goal of an application security scan is to achieve full test coverage (all the application code is tested) with the least amount of HTTP requests.

w3af needs to be able to efficiently crawl sites like this, reducing the number of HTTP requests to reach full test coverage. Some assumptions can be made:

  • Submitting the form that will favorite one product will run the same server

side code to favorite another product in the same e-commerce site.

  • Browsing /product/* pages will always run the same server side code and

show the same three HTML forms.

  • Requesting /review-comment?id=* will always return a comment.

If we believe those to be true, then we can simply request a few samples instead of all. The number of samples to collect can be configured with these misc settings are for:

  • path_max_variants: Limit how many product pages will be crawled
  • params_max_variants: Limit how many variants to sample for URLs with the same path and parameter names
  • max_equal_form_variants: Limit how many forms with the same parameters but different URLs to sample

The default should suit most of the sites, but advanced users might want to modify these settings when the scan is taking too much time or, multiple areas of the application are not being scanned and the debug log shows many messages containing the Ignoring ... simply a variant.