As Linux maintains and develops more complicated structures, variety of bugs are being reported. In this project we worked on back door in Redhat 8.0 which is the latest version in current market. We hope this study will help to maintain secure Linux system.
2. Back Door?
trapdoor: A hidden software or hardware mechanism, usually created for testing and troubleshooting, that may be used to circumvent computer security.(http://www.atis.org/tg2k/_back_door.html, 03-03-2003) Back door is usually created by a hacker in hidden place to access the system and execute critical commands. Back door usually gives a privilege to a hacker to be a root or system administrator so that the hacker can execute critical commands.
There are many kinds of shell in Unix/Linux field. We will discuss the major shells in Redhat 8.0.
BASH(Bourne Again Shell):
Bash is the shell, or command language interpreter, that will appear in the GNU operating system. Bash is an sh-compatible shell that incorporates useful features from the Korn shell (ksh) and C shell (csh). It is intended to conform to the IEEE POSIX P1003.2/ISO 9945.2 Shell and Tools standard. It offers functional improvements over sh for both programming and interactive use. In addition, most sh scripts can be run by Bash without modification. (http://220.127.116.11/search?q=cache:LRbZDn_4LtcC:www.gnu.org/software/bash/bash.html+what+is+bash&hl=ko&ie=UTF-8, 02-02-2003)
Csh is a new command language interpreter for UNIX†systems. It incorporates good features of other shells and a history mechanism similar to the redo of INTERLISP. While incorporating many features of other shells which make writing shell programs (shell scripts) easier,most of the features unique to csh are designed more for the interac-tive UNIX user. (http://www.kitebird.com/csh-tcsh-book/csh-intro.pdf, Joy Willam, 03-03-2003)
Tcsh is an enhanced, but completely compatible version of the Berkeley UNIX C shell (csh). It is a command language interpreter usable both as an interactive login shell and a shell script command processor. It includes a command-line editor, programmable word completion, spelling correction, a history mechanism, job control and a C-like syntax. (http://www.tcsh.org/Welcome, 03-03-2003) .
The ash shell is a clone of Berkeley's Bourne shell. Ash supports all of the standard sh shell commands, but is considerably smaller than bash. The ash shell lacks some features (for example, command-line histories), but needs a lot less memory. Ash could be installed if one needs a lightweight shell with many of the same capabilities as the bash shell. (http://www.firstlinux.com/cgi-bin/package/content.cgi?ID=6425, 03-03-2003)
5. History of Shell Back Doors
Redhat series represent the modern Linux operating system. Redhat has been upgraded and improved through higher versions. Redhat improved the protection against vulnerable action in the latest version 8.0, however, more bugs could be found.