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CGI Security

News Recommended Books Recommended Links Tutorials Reference CGI-scanners Selena Sol CGI scripts
CGI Security SSI Administration Debugging History Humor Etc.

CGI is a very flexible and powerful protocol, and it scales much more that most WEB developers assume.  CGI may be not that fancy technology, but it's simple and you can do almost anything it it.

The most common tool for writing CGI scripts is Perl, therefore most CGI scripts you can find on the WEB are written in this language.

Essentially, all web applications do pretty much the same things:

  1. Provide a Query Interface - Web Applications provide users with an interface for entering data. The data they enter is usually called a "query" or a "request" because the user-defined data is used to dynamically query or make a request from some service on the web server machine (searching a database, ordering a book, requesting a file).
  2. Transmit User-Defined Query - Once collected, the user-data is sent to a web server
  3. Perform Server Side Processing - The web server processes the user-data using some sort of "middleware".
  4. Massage Data - Processing almost always involves playing with data on the server. The user-defined request specifies how the data should be played with.
  5. Transmit Query Results - The processed data is now returned to the client.
  6. Perform Client Side Processing - Finally, the returned data is displayed to the user. Display might be as simple as interpreting HTML, or as complex as performing calculations, sorting, or other manipulations of the data.

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The problem with /usr/ucb/mail shell escapes is going stay with us for quite a while: I have found that many web sites run CGI helper scripts that send data from the network into /usr/ucb/mail, without censoring of, for example, newline characters embedded in the data.


Reference

CGI scripts have access to 20 or so environment variables, such as QUERY_STRING and CONTENT_LENGTH mentioned on the main page. Here's the complete list at NCSA.

REQUEST_METHOD
The HTTP method this script was called with. Generally "GET", "POST", or "HEAD".
HTTP_REFERER
The URL of the form that was submitted. This isn't always set, so don't rely on it. Don't go invading people's privacy with it, neither.
PATH_INFO
Extra "path" information. It's possible to pass extra info to your script in the URL, after the filename of the CGI script. For example, calling the URL
http://www.myhost.com/mypath/myscript.cgi/path/info/here

will set PATH_INFO to "/path/info/here". Commonly used for path-like data, but you can use it for anything.

SERVER_NAME
Your Web server's hostname or IP address (at least for this request).
SERVER_PORT
Your Web server's port (at least for this request).
SCRIPT_NAME
The path part of the URL that points to the script being executed. It should include the leading slash, but certain older Web servers leave the slash out. You can guarantee the leading slash with this line of Perl:
$ENV{'SCRIPT_NAME'}=~ s#^/?#/# ;

So the URL of the script that's being executed is, in Perl,

"http://$ENV{'SERVER_NAME'}:$ENV{'SERVER_PORT'}$ENV{'SCRIPT_NAME'}"

The complete URL the script was invoked with may also have PATH_INFO and QUERY_STRING at the end.

MIME Types

MIME types are standard, case-insensitive strings that identify a data type, used throughout the Internet for many purposes. They start with the general type of data (like text, image, or audio), followed by a slash, and end with the specific type of data (like html, gif, or jpeg). HTML files are identified with text/html, and GIFs and JPEGs are identified with image/gif and image/jpeg. Here's a pretty good list of commonly-used MIME types.


CGI-scanners

whisker.txt

R a i n F o r e s t P u p p y

Whisker
Whisker is a CGI scanner with impressive features that makes it much better than most CGI scanners.

Download:
http://www.wiretrip.net/rfp/p/doc.asp?id=21&iface=2

Xenu's Link Sleuth. Software to find broken links on a web site. Tilman Hausherr.

Common Gateway Interface (CGI) Specifications

CGI-Resources Page
CGI Tutorials and scripts


Perl Tutotial Start
CGI Scripts from NCSA
ENMPC: Tutorial on CGI
Perl and CGI Tutorial
CGI Tutorial - Frames version
Matt's Perl Tutorial
Danny Aldham's Perl CGI Tutorial Page version 1.07
Perl and CGI Tutorial
CGI Tutorial && Link
CGI Tutorial: Start
CGI Manual
CGI & Perl links on the WWW
Perl-Related Links
CGI Tutorial: A simple CGI script
CGI Tutorial: What CGI scripts are


Debugging and Troubleshooting

The Idiot's Guide to Solving Perl CGI Problems

Debugging CGI Programs contains a useful script to help debug your CGI programs. Requires Apache Server v1.2.


Administration

Seite zum Thema Linux -- SendingMirror.pl, a small script to keep your remote web server or ftp server up to date by pushing the changed data from your local host, maybe behind a firewall or a dialup line.


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Vol 25, No.12 (December, 2013) Rational Fools vs. Efficient Crooks The efficient markets hypothesis : Political Skeptic Bulletin, 2013 : Unemployment Bulletin, 2010 :  Vol 23, No.10 (October, 2011) An observation about corporate security departments : Slightly Skeptical Euromaydan Chronicles, June 2014 : Greenspan legacy bulletin, 2008 : Vol 25, No.10 (October, 2013) Cryptolocker Trojan (Win32/Crilock.A) : Vol 25, No.08 (August, 2013) Cloud providers as intelligence collection hubs : Financial Humor Bulletin, 2010 : Inequality Bulletin, 2009 : Financial Humor Bulletin, 2008 : Copyleft Problems Bulletin, 2004 : Financial Humor Bulletin, 2011 : Energy Bulletin, 2010 : Malware Protection Bulletin, 2010 : Vol 26, No.1 (January, 2013) Object-Oriented Cult : Political Skeptic Bulletin, 2011 : Vol 23, No.11 (November, 2011) Softpanorama classification of sysadmin horror stories : Vol 25, No.05 (May, 2013) Corporate bullshit as a communication method  : Vol 25, No.06 (June, 2013) A Note on the Relationship of Brooks Law and Conway Law

History:

Fifty glorious years (1950-2000): the triumph of the US computer engineering : Donald Knuth : TAoCP and its Influence of Computer Science : Richard Stallman : Linus Torvalds  : Larry Wall  : John K. Ousterhout : CTSS : Multix OS Unix History : Unix shell history : VI editor : History of pipes concept : Solaris : MS DOSProgramming Languages History : PL/1 : Simula 67 : C : History of GCC developmentScripting Languages : Perl history   : OS History : Mail : DNS : SSH : CPU Instruction Sets : SPARC systems 1987-2006 : Norton Commander : Norton Utilities : Norton Ghost : Frontpage history : Malware Defense History : GNU Screen : OSS early history

Classic books:

The Peter Principle : Parkinson Law : 1984 : The Mythical Man-MonthHow to Solve It by George Polya : The Art of Computer Programming : The Elements of Programming Style : The Unix Haterís Handbook : The Jargon file : The True Believer : Programming Pearls : The Good Soldier Svejk : The Power Elite

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The Last but not Least


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Last modified: September 12, 2017