In computing, privilege is defined as the delegation of authority to perform security-relevant functions on a computer system. A privilege allows a user to perform an action with security consequences. Examples of various privileges include the ability to create a new user, install software, or change kernel functions. Users who have been delegated extra levels of control are called privileged. Users who lack most privileges are defined as unprivileged, regular, or normal users.

Theory

Privileges can either be automatic, granted, or applied for. An automatic privilege exists when there is no requirement to have permission to perform an action. For example, on systems where people are required to log into a system to use it, logging out will not require a privilege. Systems that do not implement file protection - such as

MS-DOS MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few ope ...

- essentially give unlimited privilege to perform any action on a file. A granted privilege exists as a result of presenting some credential to the privilege granting authority. This is usually accomplished by logging on to a system with a

username A user is a person who utilizes a computer or Computer network, network Service (systems architecture), service. A user often has a user account and is identified to the system by a username (or user name). Other terms for username includ ...

and

password A password, sometimes called a passcode (for example in Apple devices), is secret data, typically a string of characters, usually used to confirm a user's identity. Traditionally, passwords were expected to be memorized, but the large number of ...

, and if the username and password supplied are correct, the user is granted additional privileges. A privilege is applied for by either an executed program issuing a request for advanced privileges, or by running some program to apply for the additional privileges. An example of a user applying for additional privileges is provided by the

sudo 



sudo ( or ) is a program for Unix-like computer operating systems that enables users to run programs with the security privileges of another user, by default the superuser. It originally stood for "superuser do", as that was all it did, and it i ...

command to run a command as superuser (''root'') user, or by the Kerberos authentication system. Modern processor architectures have multiple

CPU modes CPU modes (also called ''processor modes,'' ''CPU states,'' ''CPU privilege levels'' and other names) are operating modes for the central processing unit of some computer architectures that place restrictions on the type and scope of operations t ...

that allows the OS to run at different privilege levels. Some processors have two levels (such as ''user'' and ''supervisor'');

i386 The Intel 386, originally released as 80386 and later renamed i386, is a 32-bit microprocessor introduced in 1985. The first versions had 275,000 transistorsC, which use pointer arithmetic or do not check array bounds automatically.

Unix

Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...

systems, the superuser (commonly known as 'root') owns all the privileges. Ordinary users are granted only enough permissions to accomplish their most common tasks. UNIX systems have built-in security features. Most users cannot set up a new user account nor do other administrative procedures. The user “root” is a special user, something called super-user, which can do anything at all on the system. This high degree power is necessary to fully administer a UNIX system, but it also allows its user to make a mistake and cause system problems. Unprivileged users usually cannot: *Adjust Kernel (operating system), kernel options; *modify system files, or files of other users. *change the ownership of any files; *change the runlevel (on systems with UNIX System V, System V-style initialization); *change the file mode of any files; *adjust ulimits or disk quotas; *start, stop and remove Daemon (computing), daemons; *signal processes of other users; *create Device file, device nodes; *create or remove users or groups; *mount or unmount volumes (although it is becoming common to allow regular users to mount and unmount removable media, such as compact discs - this is typically accomplished via Filesystem in Userspace, FUSE); *execute the contents of any sbin/ directory (although it is becoming common to simply restrict the behavior of such programs when executed by regular users); *Port (computer networking), bind ports below 1024.

Windows NT

On Windows NT-based systems, privileges are delegated in varying degrees. These delegations can be defined using the local security policy manager (secpol.msc). The following is an abbreviated list of the default assignments: *'NT AUTHORITY\System' is the closest equivalent to the Superuser on Unix-like systems. It has many of the privileges of a classic Unix superuser (such as being a trustee on every file created); *'Administrator' is one of the closest equivalents to the superuser (root) on Unix-like systems. However, this user cannot override as many of the operating system's protections as the superuser can; *members of the 'Administrators' group have privileges almost equal to 'Administrator'; *members of the 'Power Users' group have the ability to install programs and backup the system. *members of the 'Users' group are the equivalent to unprivileged users on Unix-like systems. Windows defines a number of administrative privileges that can be assigned individually to users and/or groups. An account (user) holds only the privileges granted to it, either directly or indirectly through group memberships. Upon installation a number of groups and accounts are created and privileges are granted to them. However, these grants can be changed at a later time or though a Group Policy, group policy. Unlike Linux, no privileges are implicitly or permanently granted to a specific account. Some administrative privileges (e.g. taking ownership of or restoring arbitrary files) are so powerful that if used with malicious intent they could allow the entire system to be compromised. With User Account Control, user account control (on by default since Windows Vista) Windows will strip the user token of these privileges at login. Thus, if a user logs in with an account with broad system privileges, he/she will still not be ''running'' with these system privileges. Whenever the user wants to perform administrative actions requiring any of the system privileges he/she will have to do this from an ''elevated'' process. When launching an ''elevated'' process, the user is made aware that his/her administrative privileges are being asserted through a prompt requiring his/her consent. Not holding privileges until actually required is in keeping with the principle of least privilege. Elevated processes will run with the full privileges of the ''user'', not the full privileges of the ''system''. Even so, the privileges of the user may still be more than what is required for that particular process, thus not completely Principle of least privilege, least privilege. The DOS-based Windows ME, Windows 98, Windows 95 and previous versions of non-NT Windows only operated on the FAT filesystem, did not support filesystem permissions and therefore privileges are effectively defeated on Windows NT-based systems that do not use the NTFS file system.

Nomenclature

The names used in the Windows source code end in either "privilege" or "logonright". This has led to some confusion about what the full set of all these "rights" and "privileges" should be called. Microsoft currently uses the term "user rights". In the past some other terms have also been used by Microsoft, such as "privilege rights" , "logon user rights" and "nt-rights".

References

{{DEFAULTSORT:Privilege (Computing) Operating system security

Theory

Unix

Windows NT

Nomenclature

See also

References