Review webpage comments and metadata for information leakage (OTG-INFO-005)

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This article is part of the new OWASP Testing Guide v4. 
At the moment the project is in the REVIEW phase.

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Contents


Summary

It is very common, and even recommended, for programmers to include detailed comments and metadata on their source code. However, comments and metadata included into the HTML code might reveal, to a potential attacker, internal information that should not be available to them. Comments and metadata review should be done in order to determine if any information is being leaked.

Test Objectives

Review webpage comments and metadata to better understand the application and to find any information leakage.

HTML comments are also used by the developers to include debugging information about the application. Sometimes they forget about the comments and they leave them on in production. You should look for HTML comments which start with "<!--" and end with "-->".

How to Test

Black Box testing and example

Check HTML source code for comments containing sensitive information which can help the attacker gain more insight about the application. It might be SQL code, usernames and passwords, internal IP addresses, or debugging information.

...

<div class="table2">
  <div class="col1">1</div><div class="col2">Mary</div>
  <div class="col1">2</div><div class="col2">Peter</div>
  <div class="col1">3</div><div class="col2">Joe</div>

<!-- Query: SELECT id, name FROM app.users WHERE active='1' -->

</div>
...

You could even find something like this:

<!-- Use the DB administrator password for testing:  f@keP@a$$w0rD -->

Check HTML version information for valid version numbers and Data Type Definition (DTD) URLs

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
  • "strict.dtd" -- default strict DTD
  • "loose.dtd" -- loose DTD
  • "frameset.dtd" -- DTD for frameset documents

Some Meta tags do not provide active attack vectors but instead allow an attacker to profile an application to

<META name="Author" content="Andrew Muller">

Some Meta tags alter HTTP response headers, such as http-equiv which sets an HTTP response header based on the the content attribute of a meta element, such as:

<META http-equiv="Expires" content="Fri, 21 Dec 2012 12:34:56 GMT">

which will result in the HTTP header:

Expires: Fri, 21 Dec 2012 12:34:56 GMT

and

<META http-equiv="Cache-Control" content="no-cache">

will result in

Cache-Control: no-cache

Test to see if this can be used to conduct injection attacks (e.g. CRLF attack). It can also help determine the level of data leakage via the browser cache.

A common (but not WCAG compliant) Meta tag is the refresh.

<META http-equiv="Refresh" content="15;URL=https://www.owasp.org/index.html">

A common use for Meta tag is to specify keywords that a search engine may use to improve the quality of search results.

<META name="keywords" lang="en-us" content="OWASP, security, sunshine, lollipops">

Although most webservers manage search engine indexing via the robots.txt file, it can also be managed by Meta tags. The tag below will advise robots to not index and not follow links on the HTML page containing the tag.

<META name="robots" content="none">

The Platform for Internet Content Selection (PICS) and Protocol for Web Description Resources (POWDER) provide infrastructure for associating meta data with Internet content.


Gray Box testing and example

Not applicable.

Tools

  • Wget
  • Browser "view source" function
  • Eyeballs
  • Curl

References

Whitepapers

[1] http://www.w3.org/TR/1999/REC-html401-19991224 HTML version 4.01

[2] http://www.w3.org/TR/2010/REC-xhtml-basic-20101123/ XHTML (for small devices)

[3] http://www.w3.org/TR/html5/ HTML version 5