Why should not I add current directory to PATH in Linux?

[shivajikobardan]

TL;DR Summary

Why should not I add current directory to PATH in Linux?

I get that if I put current directory in PATH like said above, I can execute commands from any directory. But what's the problem in that? How's other person able to come and execute it? Why does it makes system unsecure compared to the case where we don't put current directory to PATH? Can you explain the example he's telling?

 

[jtbell]

To make his example more explicit, suppose that the directory you're currently in, has a program (put there by some sneaky person) named ls, that reformats your disk, or encrypts it with a secret password, or something like that. You decide to find out what files are in the directory, and type the usual ls command. It runs the sneaky ls instead of the normal ls command which is something like /usr/bin/ls.

 

[pasmith]

In that example, the system will look in the current directory before looking in /bin or /usr/bin. It will therefore run the dodgy ./ls rather than the authentic /bin/ls. And the malicious user can modify ./ls so it doesn't list itself when imitating the output of /bin/ls.

This can be mitigated by placing . at the end of $PATH rather than the beginning.

 

[shivajikobardan]

In that example, the system will look in the current directory before looking in /bin or /usr/bin. It will therefore run the dodgy ./ls rather than the authentic /bin/ls. And the malicious user can modify ./ls so it doesn't list itself when imitating the output of /bin/ls.

This can be mitigated by placing . at the end of $PATH rather than the beginning.

thank you. I got this now.