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Enhancing Web Security and Shell Scripting with ModSecurity and wget

This chapter delves into the implementation of ModSecurity, an open-source intrusion detection and prevention engine for web applications, and its role in safeguarding web servers from attacks like directory traversal and wget exploits. It explains how user agents function within HTTP requests and provides practical exercises using wget and grep commands to manipulate and analyze text files. Additionally, the chapter covers the use of shell scripts for executing commands, including methods to document and organize scripts for better usability and maintenance.

marcellus-alston
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Enhancing Web Security and Shell Scripting with ModSecurity and wget

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  1. Chapter Five (Continued) And some class exercises

  2. But first…why wget did not work • A few months ago I added a module to my apache server called ModSecurity • ModSecurity is an open source intrusion detection and prevention engine for web applications • Operating as an Apache Web server module or standalone, the purpose of ModSecurity is to increase web application security, protecting web applications from known and unknown attacks.

  3. The Threat - wget • Many web exploits take advantage of flaws in coding to use directory transversal as a means to execute programs such as wget • directory transversal is essentially http://rose.edu/../../bin/wget yada yada • Various combinations are tried until one succeeds (we will look at an actual attack later in the course) • But ModSecurity protects against wget attacks (well sort of…)

  4. wget and User-Agent • A user agent is the client application used with a particular network protocol • Web user agents range from web browsers to search engine crawlers ("spiders"), etc. • When Internet users visit a web site, a text string is generally sent to identify the user agent to the server.

  5. wget and User-Agent • This forms part of the HTTP request, prefixed with User-agent: or User-Agent: • wget has a command line option (-U) to modify or erase the User-Agent sent to server

  6. Exercise • Use the following command to download the gettysburg.txt file to your class workstation: wget –U “” http://wildbill.org/gettysburg.txt • Now use wc determine: • The number of lines in the file • The number of words in the file • The number of characters in the file

  7. Grep Exercise • Using grep try the following: grep four gettysburg.txt Ok now try: grep –i four gettysburg.txt Now look at the man page for grep…lot’s of options!

  8. Using the Manipulate and Format Commands • These commands are: tr and pr • Used to edit and transform the appearance of data before it is displayed or printed

  9. Translating CharactersUsing the tr command • tr copies data from the standard input to the standard output, substituting or deleting characters specified by options and patterns • The patterns are strings and the strings are sets of characters • A popular use of tr is converting lowercase characters to uppercase

  10. tr Exercise • Type the following: tr t 0 < gettysburg.txt tr a-z A-Z < gettysburg.txt

  11. Using the pr Command toFormat Your Output • pr prints specified files on the standard output in paginated form • By default, pr formats the specified files into single-column pages of 66 lines • Each page has a five-line header, its latest modification date, current page, and five-line trailer consisting of blank lines

  12. Pr Exercise • Type the following: pr gettysburg.txt pr –header=“GBA Ver 1.0” gettysburg.txt pr –t gettysburg.txt pr – t –d gettysburg.txt

  13. Using a Shell Script toImplement the Application • Shell scripts should contain: • The commands to execute • Comments to identify and explain the script so that users or programmers other than the author can understand how it works • Use the pound (#) character to mark comments in a script file

  14. Running a Shell Script • The Bash shell accepts more variations in command structures that other UNIX shells thus it is more popular • You can run a shell script by typing sh followed by the name of the script, or make the script executable and type ./ prior to the script name sh filename.sh or ./filename.sh

  15. Shell Script Discussion… • First line… #!/bin/bash • Uses: • Combine lengthy and repetitive sequences of commands into a single, simple command. • Create new commands using combinations of utilities in ways the original authors never thought of. • Simple shell scripts might be written as shell aliases, but the script can be made available to all users and all processes. Shell aliases apply only to the current shell. • Wrap programs over which you have no control inside an environment that you can control. • Rapid prototyping (but avoid letting prototypes become production)

  16. Shell Script Discussion… • For easier reading use all UPPERCASE names for variables • # Use the comment character to add information to your scripts

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