Using search engines such as Google, “search engine hackers” can easily find exploitable targets and sensitive data. This article outlines some of the techniques used by hackers and discusses how to prevent your site from becoming a victim of this form of information leakage.Other Articles By Johnny Long.

The Google curious search engine found at http://www.google.com/ offers many features, including language and document translation; web, image, newsgroups, catalog, and news searches; and more. These features offer obvious benefits to even the most uninitiated web surfer, but these same features offer far more nefarious possibilities to the most malicious Internet users, including hackers, computer criminals, identity thieves, and even terrorists. This article outlines the more harmful applications of the Google search engine, techniques that have collectively been termed “Google hacking.” The intent of this article is to educate web administrators and the security community in the hopes of eventually stopping this form of information leakage. This document is an excerpt of the full Google Hacker’s Guide published by Johnny Long, and located at http://johnny.ihackstuff.com/.

Basic Search TechniquesSince the Google web interface is so easy to use, I won’t describe the basic functionality of the http://www.google.com/ web page. Instead, I’ll focus on the various operators available:

Use the plus sign (+) to force a search for an overly common word. Use the minus sign (-) to exclude a term from a search. No space follows these signs.

To search for a phrase, supply the phrase surrounded by double quotes (” “).

A period (.) serves as a single-character wildcard.

An asterisk (*) represents any word–not the completion of a word, as is traditionally used.

Google advanced operators help refine searches. Advanced operators use a syntax such as the following:

operator:search_termNotice that there’s no space between the operator, the colon, and the search term.

The site: operator instructs Google to restrict a search to a specific web site or domain. The web site to search must be supplied after the colon.

The filetype: operator instructs Google to search only within the text of a particular type of file. The file type to search must be supplied after the colon. Don’t include a period before the file extension.

The link: operator instructs Google to search within hyperlinks for a search term.

The cache: operator displays the version of a web page as it appeared when Google crawled the site. The URL of the site must be supplied after the colon.

The intitle: operator instructs Google to search for a term within the title of a document.

The inurl: operator instructs Google to search only within the URL (web address) of a document. The search term must follow the colon.

Google Hacking Mini-GuideBy Johnny Long.Date: May 7, 2004.Google Hacking TechniquesBy using the basic search techniques combined with Google’s advanced operators, anyone can perform information-gathering and vulnerability-searching using Google. This technique is commonly referred to as Google hacking.

Site MappingTo find every web page Google has crawled for a specific site, use the site: operator. Consider the following query:

site:http://www.microsoft.com microsoftThis query searches for the word microsoft, restricting the search to the http://www.microsoft.com/ web site. How many pages on the Microsoft web server contain the word microsoft? According to Google, all of them! Google searches not only the content of a page, but the title and URL as well. The word microsoft appears in the URL of every page on http://www.microsoft.com/. With a single query, an attacker gains a rundown of every web page on a site cached by Google.

There are some exceptions to this rule. If a link on the Microsoft web page points back to the IP address of the Microsoft web server, Google will cache that page as belonging to the IP address, not the http://www.microsoft.com/ web server. In this special case, an attacker would simply alter the query, replacing the word microsoft with the IP address(es) of the Microsoft web server.

Finding Directory ListingsDirectory listings provide a list of files and directories in a browser window instead of the typical text-and graphics mix generally associated with web pages. These pages offer a great environment for deep information gathering.
Locating directory listings with Google is fairly straightforward. Figure 1 shows that most directory listings begin with the phrase Index of, which also shows in the title. An obvious query to find this type of page might be intitle:index.of, which may find pages with the term index of in the title of the document. Unfortunately, this query will return a large number of false positives, such as pages with the following titles:

Index of Native American Resources on the Internet

LibDex–Worldwide index of library catalogues

Iowa State Entomology Index of Internet Resources

Judging from the titles of these documents, it’s obvious that not only are these web pages intentional, they’re also not the directory listings we’re looking for. Several alternate queries provide more accurate results:

intitle:index.of “parent directory”intitle:index.of name sizeThese queries indeed provide directory listings by not only focusing on index.of in the title, but on keywords often found inside directory listings, such as parent directory, name, and size. Obviously, this search can be combined with other searches to find files of directories located in directory listings.

Versioning: Obtaining the Web Server Software/VersionThe exact version of the web server software running on a server is one piece of information an attacker needs before launching a successful attack against that web server. If an attacker connects directly to that web server, the HTTP (web) headers from that server can provide this essential information. It’s possible, however, to retrieve similar information from Google’s cache without ever connecting to the target server under investigation. One method involves using the information provided in a directory listing.

This example was gathered using the following query:

intitle:index.of server.atThis query focuses on the term index of in the title and server at appearing at the bottom of the directory listing. This type of query can also be pointed at a particular web server:

intitle:index.of server.at site:aol.comThe result of this query indicates that gprojects.web.aol.com and vidup-r1.blue.aol.com both run Apache web servers.

It’s also possible to determine the version of a web server based on default pages installed on that server. When a web server is installed, it generally will ship with a set of default web pages, like the Apache 1.2.6.

These pages can make it easy for a site administrator to get a web server running. By providing a simple page to test, the administrator can simply connect to his own web server with a browser to validate that the web server was installed correctly. Some operating systems even come with web server software already installed. In this case, an Internet user may not even realize that a web server is running on his machine. This type of casual behavior on the part of an Internet user will lead an attacker to rightly assume that the web server is not well maintained, and by extension is insecure. By further extension, the attacker can assume that the entire operating system of the server may be vulnerable by virtue of poor maintenance.

The following table provides a brief rundown of some queries that can locate various default pages.

Apache Server Version Query Apache 1.3.0-1.3.9 Intitle:Test.Page.for.Apache It.worked! this.web.site! Apache 1.3.11-1.3.26 Intitle:Test.Page.for.Apache seeing.this.instead Apache 2.0 Intitle:Simple.page.for.Apache Apache.Hook.Functions Apache SSL/TLS Intitle:test.page “Hey, it worked !” “SSL/TLS-aware” Many IIS servers intitle:welcome.to intitle:internet IIS Unknown IIS server intitle:”Under construction” “does not currently have” IIS 4.0 intitle:welcome.to.IIS.4.0 IIS 4.0 allintitle:Welcome to Windows NT 4.0 Option Pack IIS 4.0 allintitle:Welcome to Internet Information Server IIS 5.0 allintitle:Welcome to Windows 2000 Internet Services IIS 6.0 allintitle:Welcome to Windows XP Server Internet Services Many Netscape servers allintitle:Netscape Enterprise Server Home Page Unknown Netscape server allintitle:Netscape FastTrack Server Home Page

Using Google as a CGI ScannerTo accomplish its task, a CGI scanner must know what exactly to search for on a web server. Such scanners often utilize a data file filled with vulnerable files and directories like the one shown below:

/cgi-bin/cgiemail/uargg.txt

/random_banner/index.cgi

/random_banner/index.cgi

/cgi-bin/mailview.cgi

/cgi-bin/maillist.cgi

/cgi-bin/userreg.cgi

/iissamples/ISSamples/SQLQHit.asp

/iissamples/ISSamples/SQLQHit.asp

/SiteServer/admin/findvserver.asp

/scripts/cphost.dll/cgi-bin/finger.cgi

Combining a list like this one with a carefully crafted Google search, Google can be used as a CGI scanner. Each line can be broken down and used in either an index.of or inurl search to find vulnerable targets. For example, a Google search for this:

allinurl:/random_banner/index.cgi

A hacker can take sites returned from this Google search, apply a bit of hacker “magic,” and eventually get the broken random_banner program to cough up any file on that web server, including the password file.