UNIX Security 2.ppt.pptVIP

October 15, 2002 Serguei A. Mokhov, mokhov@cs.concordia.ca UNIX Security 2: A Quick Recap SOEN321 - Information Systems Security Revision 1.3 Date: September 30, 2003 Trojan Horse In UNIX, as in many other OS, there are ways to allow users execution of programs written by other users. By having those programs executed in such a way that it provides the access rights of the executing user, the other users may misuse these rights. Trojan Horse (2) Examples: A text editor searching for keywords in the open file; upon successful match, copies the document elsewhere. The code that missuses its runtime environment, is called a Trojan Horse. UNIX path search. We’ll explore this one in greater detail. A program emulating login. UNIX path Long search paths, which are very common in UNIX, make Trojan Horse matters worse. Recall COMP346, Operating Systems... PA1... “... to set proper Java version change your path to ....” The users can configure their environment variables in their .cshrc, .tcshrc, .bashrc, whatever, including the path variable. UNIX path (2) The search path lists the set of the directories to search when an ambiguous command name given (i.e. not not absolute, which comprises 99% of the commands). When user types a command in the shell’s prompt, the shell starts looking at every item in the path list, to look up the actual command. The first command found is executed... UNIX path (3) Obviously (to whom? :-)), all the directories the path list must be secure; otherwise, a Trojan Horse replacement of a common command can be executed accidentally if it happened to sneak into one of those directories in the path. A bad habit is to have “.” in your path list. UNIX path (4) “.” means current directory, so if you type a command, say ls, and a corresponding fake ls happened to be in your current directory, you can get in trouble. Example: a “friend” shares with you a directory; by being in it and executing a command, you can actually execute the one in your “friend”