ls -l /etc/passwd
$ ls -l /etc/passwd -rw-r--r-- 1 root root 1862 2011-06-15 21:59 /etc/passwd
So an ordinary user can read the file. Is this a security hole?
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Typically, the hashed passwords are stored in
/etc/shadow on most Linux systems:
-rw-r----- 1 root shadow 1349 2011-07-03 03:54 /etc/shadow
(They are stored in
/etc/master.passwd on BSD systems.)
Programs that need to perform authentication still need to run with
-rwsr-xr-x 1 root root 42792 2011-02-14 14:13 /usr/bin/passwd
If you dislike the
setuid root programs and one single file containing all the hashed passwords on your system, you can replace it with the Openwall TCB PAM module. This provides every single user with their own file for storing their hashed password -- as a result the number of
setuid root programs on the system can be drastically reduced.
To some extent it is, as you can identify users. In the past you could also pick up their passwords. However, the one userid really worth cracking is
root which is well known without the password file.
The utility of having the password file world readable generally far outweighs the risk. Even if it weren't world readable, a functioning
getent passwd command would render the security gain void.
The ability for non-root users to identify files owned by others would disappear. Being able to identify owned (user in passwd file) and unowned files (user not in passwd file) can be useful in reviewing the contents of a file system. While it would be possible to resolve this with appropriate
setuid programs, that would add a huge attack vector via those programs.
In the end it is a matter of balance, and in this case I would say the balance is firmly on having password world readable.