DISCUSSION [NIST SP 800-171 R2]
Identifiers are provided for users, processes acting on behalf of users, or devices (IA.L1-3.5.1). Preventing reuse of identifiers implies preventing the assignment of previously used individual, group, role, or device identifiers to different individuals, groups, roles, or devices.
FURTHER DISCUSSION
Identifiers uniquely associate a user ID to an individual, group, role, or device. Establish guidelines and implement mechanisms to prevent identifiers from being reused for the period of time established in the policy.
Example
As a system administrator, you maintain a central directory/domain that holds the accounts for users, computers, and network devices. As part of your job, you issue unique usernames (e.g., riley@acme.com) for the staff to access resources. When you issue staff computers you also rename the computer to reflect to whom it is assigned (e.g., riley-laptop01). Riley has recently left the organization, so you must manage the former staff member’s account. Incidentally, their replacement is also named Riley. In the directory, you do not assign the previous account to the new user, as policy has defined an identifier reuse period of 24 months [a]. In accordance with policy, you create an account called riley02 [b]. This account is assigned the appropriate permissions for the new user. A new laptop is also provided with the identifier of riley02-laptop01.
Potential Considerations
Are accounts uniquely assigned to employees, contractors, and subcontractors [b]? 40
Are account identifiers reused [b]?41
Copyright
Copyright 2020, 2021 Carnegie Mellon University and The Johns Hopkins University Applied Physics Laboratory LLC.
Copyright 2021 Futures, Inc.
This material is based upon work funded and supported by the Department of Defense under Contract No. FA8702-15-D-0002 with Carnegie Mellon University for the operation of the Software Engineering Institute, a federally funded research and development center, and under Contract No. HQ0034-13-D-0003 and Contract No. N00024-13-D-6400 with the Johns Hopkins University Applied Physics Laboratory LLC, a University Affiliated Research Center.
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