11-23-2006
The point we are making is this:
With chmod 777, you are giving all rights on all the files to ANY user.
Lets say a hacker managed to find an exploit which allows him to gain some kind of access to your server through a vulnerable service, which allows him to execute code as the user of the service.
If the last 6/7 is there it means he can change your files regardless of which user he gets access as. (The keys are in the car)
With the second 6/7 if means that anyone in the group can change the files. (You given someone the valet key to the car)
With only the first 6/7 you (the owner) only can make the changes. ( the key to the car is in your pocket)
So as you can see, someone malicious has more to do in each case, before they can change your files.
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CHMOD(1) General Commands Manual CHMOD(1)
NAME
chmod - change mode
SYNOPSIS
chmod mode file ...
DESCRIPTION
The mode of each named file is changed according to mode, which may be absolute or symbolic. An absolute mode is an octal number con-
structed from the OR of the following modes:
4000 set user ID on execution
2000 set group ID on execution
1000 sticky bit, see chmod(2)
0400 read by owner
0200 write by owner
0100 execute (search in directory) by owner
0070 read, write, execute (search) by group
0007 read, write, execute (search) by others
A symbolic mode has the form:
[who] op permission [op permission] ...
The who part is a combination of the letters u (for user's permissions), g (group) and o (other). The letter a stands for ugo. If who is
omitted, the default is a but the setting of the file creation mask (see umask(2)) is taken into account.
Op can be + to add permission to the file's mode, - to take away permission and = to assign permission absolutely (all other bits will be
reset).
Permission is any combination of the letters r (read), w (write), x (execute), s (set owner or group id) and t (save text - sticky). Let-
ters u, g or o indicate that permission is to be taken from the current mode. Omitting permission is only useful with = to take away all
permissions.
The first example denies write permission to others, the second makes a file executable:
chmod o-w file
chmod +x file
Multiple symbolic modes separated by commas may be given. Operations are performed in the order specified. The letter s is only useful
with u or g.
Only the owner of a file (or the super-user) may change its mode.
SEE ALSO
ls(1), chmod(2), chown (1), stat(2), umask(2)
CHMOD(1)