Get a MacBook Air with Online Courses Now

Critical Security Control: 15

Critical Security Control: 15

Controlled Access Based on the Need to Know

The processes and tools used to track/control/prevent/correct secure access to critical assets (e.g., information, resources, systems) according to the formal determination of which persons, computers, and applications have a need and right to access these critical assets based on an approved classification.

Why Is This Control Critical?

Some organizations do not carefully identify and separate their most sensitive and critical assets from less sensitive, publicly accessible information on their internal networks. In many environments, internal users have access to all or most of the critical assets. Sensitive assets may also include systems that provide management and control of physical systems (e.g., SCADA). Once attackers have penetrated such a network, they can easily find and exfiltrate important information, cause physical damage, or disrupt operations with little resistance. For example, in several high-profile breaches over the past two years, attackers were able to gain access to sensitive data stored on the same servers with the same level of access as far less important data. There are also examples of using access to the corporate network to gain access to, then control over, physical assets and cause damage.

How to Implement This Control

ID # Description Category
CSC 15-1 Locate any sensitive information on separated VLANS with firewall filtering. All communication of sensitive information over less-trusted networks should be encrypted. Quick win
CSC 15-3 Enforce detailed audit logging for access to nonpublic data and special authentication for sensitive data. Visibility/Attribution
CSC 15-4 Segment the network based on the trust levels of the information stored on the servers. Whenever information flows over a network with a lower trust level, the information should be encrypted. Configuration/Hygiene
CSC 15-5 Use host-based data loss prevention (DLP) to enforce ACLs even when data is copied off a server. In most organizations, access to the data is controlled by ACLs that are implemented on the server. Once the data have been copied to a desktop system, the ACLs are no longer enforced and the users can send the data to whomever they want. Advanced

CSC 15 Procedures and Tools

It is important that an organization understand what its sensitive information is, where it resides, and who needs access to it. To derive sensitivity levels, organizations need to put together a list of the key types of data and the overall importance to the organization. This analysis would be used to create an overall data classification scheme for the organization. At a base level, a data classification scheme is broken down into two levels: public (unclassified) and private (classified). Once the private information has been identified, it can then be further subdivided based on the impact it would have to the organization if it were compromised.

Once the sensitivity of the data has been identified, the data need to be traced back to business applications and the physical servers that house those applications. The network then needs to be segmented so that systems of the same sensitivity level are on the same network and segmented from systems with different trust levels. If possible, firewalls need to control access to each segment. If data are flowing over a network with a lower trust level, encryption should be used.

Job requirements should be created for each user group to determine what information the group needs access to in order to perform its jobs. Based on the requirements, access should only be given to the segments or servers that are needed for each job function. Detailed logging should be turned on for all servers in order to track access and examine situations where someone is accessing data that they should not be accessing.

CSC 15 Effectiveness Metrics

In order to test the effectiveness of the automated implementation of this control, organizations should measure the following:

1. Can the system detect all attempts by users to access files on local systems or network-accessible file shares without the appropriate privileges (yes or no)?

2. How long does it take the system to generate an alert or e-mail for administrative personnel of a user inappropriately accessing the file shares (time in minutes)?

CSC 15 Automation Metrics

In order to automate the collection of relevant data from these systems, organizations should gather the following information with automated technical sensors:

1. What percentage of the organization's data sets have not been classified in accordance with the organization's data classification standards (by business unit)?

2. What percentage of sensitive data sets are not configured to require logging of access to the data set (by business unit)?

3. What percentage of the organization's business systems are not utilizing host based Data Loss Prevention (DLP) software applications (by business unit)?

CSC 15 Effectiveness Test

To evaluate the implementation of Control 15 on a periodic basis, the evaluation team must create two test accounts each on 10 representative systems in the enterprise: five server machines and five client systems. For each system evaluated, one account must have limited privileges, while the other must have privileges necessary to create files on the systems. The evaluation team must then verify that the non-privileged account is unable to access the files created for the other account on the system. The team must also verify that an alert or e-mail is generated based on the attempted unsuccessful access within 24 hours. Upon completion of the test, these accounts must be removed.

CSC 15 System Entity Relationship Diagram

Organizations will find that by diagramming the entities necessary to fully meet the goals defined in this control, it will be easier to identify how to implement them, test the controls, and identify where potential failures in the system might occur.

A control system is a device or set of devices used to manage, command, direct, or regulate the behavior of other devices or systems. In this case, the data classification system and permission baseline is the blueprint for how authentication and access of data is controlled. The following list of the steps in the above diagram shows how the entities work together to meet the business goal defined in this control. The list also delineates each of the process steps in order to help identify potential failure points in the overall control.

Step 1: An appropriate data classification system and permissions baseline applied to production data systems

Step 2: Access appropriately logged to a log management system

Step 3: Proper access control applied to portable media/USB drives

Step 4: Active scanner validates, checks access, and checks data classification

Step 5: Host-based encryption and data-loss prevention validates and checks all access requests.


Creative Commons - Attribution-NoDerivs 3.0 Unported (CC BY-ND 3.0)

This work is licensed under a Creative Commons Attribution-NoDerivs 3.0 Unported License.

To further clarify the Creative Commons license related to the 20 Critical Controls content, (i) All persons are authorized to use the content as a framework in their organization or to sell professional services related to the content (e.g. a consulting engagement to implement the 20 Critical Controls), and (ii) sale of the contents as a framework model is not authorized. Users of the 20 Critical Controls framework are also required to refer to http://www.sans.org/critical-security-controls/ when referring to the 20 Critical Controls in order to ensure that users are employing the most up to date guidance.