3.4.8 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.

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.