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The /etc/passwd file can be thought of as a simple flat database that lists all of the users on the system. It is possible to configure a Unix system to use other directory services, such as NIS, LDAP, and/or Kerberos. When these systems are used, the Unix operating system is often modified so that the system programs and applications are can still think that all of the account information still reside in a /etc/passwd file. In a way they create virtual /etc/passwd file. If LDAP became unavailable the authentication goes back to passwd authentication.
On most Unix systems the passwords for these accounts are kept in a file named /etc/shadow, or /etc/security/passwd. T
newkey -u usernameOr, you can create an entry in the database for the nobody user account, and then any user can run the chkey program to create their own entries in the database without logging in as root.
Each flavor of Unix provides a default set of system special user accounts that prevents the root and system accounts from owning all operating system files and file systems.
Attention: Use caution when removing a system special user account. You can disable a specific account by inserting an asterisk (*) at the beginning of its corresponding line of the /etc/shadow file. However, be careful not to disable the root user account. If you remove system special user accounts or disable the root account, the operating system will not function.
During installation of the operating system, a number of default user and group IDs are created. Depending on the applications you are running on your system and where your system is located in the network, some of these user and group IDs can become security weaknesses, vulnerable to exploitation. If these users and group IDs are not needed, you can remove them to minimize security risks associated with them.
The following table lists the most common default user IDs that you might be able to remove:
|uucp, nuucp||Owner of hidden files used by uucp protocol. The uucp user account is used for the UNIX-to-UNIX Copy Program, which is a group of commands, programs, and files, present on most AIX systems, that allows the user to communicate with another AIX system over a dedicated line or a telephone line.|
|lpd||Owner of files used by printing subsystem|
|guest||Allows access to users who do not have access to accounts|
The following table lists common groups that might not be needed:
|uucp||Group to which uucp and nuucp users belong|
|printq||Group to which lpd user belongs|
Analyze your system to determine which IDs are indeed not needed. There might also be additional user and group IDs that you might not need. Before your system goes into production, perform a thorough evaluation of available IDs.
|User Name||User ID||Description|
|daemon||1||Umbrella system daemon associated with routine system tasks.|
|bin||2||Administrative daemon associated with running system binaries to perform some routine system task.|
|sys||3||Administrative daemon associated with system logging or updating files in temporary directories.|
|adm||4||Administrative daemon associated with system logging.|
|lp||71||Line printer daemon.|
|uucp||5||Daemon associated with uucp functions.|
|nuucp||6||Daemon associated with uucp functions.|
|smmsp||25||Sendmail message submission program daemon.|
|listen||37||Network listener daemon.|
|nobody||60001||Assigned to users or software processes that do not need nor should have any special permissions.|
|noaccess||60002||Assigned to a user or a process that needs access to a system through some application but without actually logging in.|
|nobody4||65534||SunOS 4.0 or 4.1 version of the nobody user account.|
In Table 2-1, you'll find the standard users set up by the installation process (this is essentially the /etc/passwd file). The Group ID (GID) in this table is the primary group for the user. See the section called User Private Groups for details on how groups are used.
Table 2-1. Standard Users
User UID GID Home Directory Shell root 0 0 /root /bin/bash bin 1 1 /bin daemon 2 2 /sbin adm 3 4 /var/adm lp 4 7 /var/spool/lpd sync 5 0 /sbin /bin/sync shutdown 6 0 /sbin /sbin/shutdown halt 7 0 /sbin /sbin/halt 8 12 /var/spool/mail news 9 13 /var/spool/news uucp 10 14 /var/spool/uucp operator 11 0 /root games 12 100 /usr/games gopher 13 30 /usr/lib/gopher-data ftp 14 50 /home/ftp nobody 99 99 /
This is not strictly openldap, but it should be a common problem. I am
suprised nobody ran into this earlier.
Here is an interesting inter-nonoperability issue. So I used the migrate scripts from PADL to dump NIS+ user and group maps into an LDAP directory.
Well and good. However, Solaris stores the primary group membership information in the gid field in the passwd map. As Unix usually does. :)
Enter auth_ldap, authentication module for Apache. When I use the "require valid group" directive, the code searches the group entry for the "member"
attribute with the value of the current user. The trouble is, there usually are none, because the group map on NIS+ did not define it, except in the
case of secondary groups.
Not that it's very diffucult to manually hack this, but there has got to be an official solution!
Thanks in advance,
Simon (Vsevolod ILyushchenko) email@example.com
Security Guide - Security Guide Aix52 security guide
Security Guide - System Special User Accounts
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