CGI Security

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.

• WWW Security FAQ CGI Scripts

• WWW Security FAQ Safe Scripting in Perl

• WEBsmith Issue 2 CGI Security

• CGI Security

• Server Side Includes and CGI Security

• The Common Gateway Interface Security

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

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.

Etc

Etc

Society

Groupthink : Two Party System as Polyarchy : Corruption of Regulators : Bureaucracies : Understanding Micromanagers and Control Freaks : Toxic Managers :   Harvard Mafia : Diplomatic Communication : Surviving a Bad Performance Review : Insufficient Retirement Funds as Immanent Problem of Neoliberal Regime : PseudoScience : Who Rules America : Neoliberalism  : The Iron Law of Oligarchy : Libertarian Philosophy

Quotes

War and Peace : Skeptical Finance : John Kenneth Galbraith :Talleyrand : Oscar Wilde : Otto Von Bismarck : Keynes : George Carlin : Skeptics : Propaganda  : SE quotes : Language Design and Programming Quotes : Random IT-related quotes :  Somerset Maugham : Marcus Aurelius : Kurt Vonnegut : Eric Hoffer : Winston Churchill : Napoleon Bonaparte : Ambrose Bierce :  Bernard Shaw : Mark Twain Quotes

Bulletin:

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 DOS :  Programming Languages History : PL/1 : Simula 67 : C : History of GCC development :  Scripting 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-Month :  How to Solve It by George Polya : The Art of Computer Programming : The Elements of Programming Style : The Unix Hater’s Handbook : The Jargon file : The True Believer : Programming Pearls : The Good Soldier Svejk : The Power Elite

Most popular humor pages:

Manifest of the Softpanorama IT Slacker Society : Ten Commandments of the IT Slackers Society : Computer Humor Collection : BSD Logo Story : The Cuckoo's Egg : IT Slang : C++ Humor : ARE YOU A BBS ADDICT? : The Perl Purity Test : Object oriented programmers of all nations : Financial Humor : Financial Humor Bulletin, 2008 : Financial Humor Bulletin, 2010 : The Most Comprehensive Collection of Editor-related Humor : Programming Language Humor : Goldman Sachs related humor : Greenspan humor : C Humor : Scripting Humor : Real Programmers Humor : Web Humor : GPL-related Humor : OFM Humor : Politically Incorrect Humor : IDS Humor : "Linux Sucks" Humor : Russian Musical Humor : Best Russian Programmer Humor : Microsoft plans to buy Catholic Church : Richard Stallman Related Humor : Admin Humor : Perl-related Humor : Linus Torvalds Related humor : PseudoScience Related Humor : Networking Humor : Shell Humor : Financial Humor Bulletin, 2011 : Financial Humor Bulletin, 2012 : Financial Humor Bulletin, 2013 : Java Humor : Software Engineering Humor : Sun Solaris Related Humor : Education Humor : IBM Humor : Assembler-related Humor : VIM Humor : Computer Viruses Humor : Bright tomorrow is rescheduled to a day after tomorrow : Classic Computer Humor

The Last but not Least Technology is dominated by two types of people: those who understand what they do not manage and those who manage what they do not understand ~Archibald Putt. Ph.D

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Last modified: March 12, 2019