3.4.8

Requirement

Apply deny-by-exception (blacklisting) policy to prevent the use of unauthorized software or deny-all, permit-by-exception (whitelisting) policy to allow the execution of authorized software.

Discussion

The process used to identify software programs that are not authorized to execute on systems is commonly referred to as blacklisting. The process used to identify software programs that are authorized to execute on systems is commonly referred to as whitelisting. Whitelisting is the stronger of the two policies for restricting software program execution. In addition to whitelisting, organizations consider verifying the integrity of whitelisted software programs using, for example, cryptographic checksums, digital signatures, or hash functions. Verification of whitelisted software can occur either prior to execution or at system startup. [SP 800-167] provides guidance on application whitelisting.

NIST 800-171A Assessment Guidance

Examine

[SELECT FROM: Configuration management policy; procedures addressing least functionality in the system; security plan; configuration management plan; system design documentation; system configuration settings and associated documentation; list of software programs not authorized to execute on the system; list of software programs authorized to execute on the system; security configuration checklists; review and update records associated with list of authorized or unauthorized software programs; change control records; system audit logs and records; other relevant documents or records].
Interview

[SELECT FROM: Personnel with responsibilities for identifying software authorized or not authorized to execute on the system; personnel with information security responsibilities; system or network administrators].
Test

[SELECT FROM: Organizational process for identifying, reviewing, and updating programs authorized or not authorized to execute on the system; process for implementing blacklisting or whitelisting; mechanisms supporting or implementing blacklisting or whitelisting].

ID	Assessment Objectives
3.4.8[a]	A policy specifying whether whitelisting or blacklisting is to be implemented is specified.
3.4.8[b]	The software allowed to execute under whitelisting or denied use under blacklisting is specified.
3.4.8[c]	Whitelisting to allow the execution of authorized software or blacklisting to prevent the use of unauthorized software is implemented as specified.

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