2 cissp ® Official Study Guide Eighth Edition

Patch Management 
Patch
is a blanket term for any type of code written to correct a bug or vulnerability or 
improve the performance of existing software. The software can be either an operating 
system or an application. Patches are sometimes referred to as updates, quick fi xes, and 
hot fi xes. In the context of security, administrators are primarily concerned with security 
patches, which are patches that affect the vulnerability of a system. 
Even though vendors regularly write and release patches, these patches are useful 
only if they are applied. This may seem obvious, but many security incidents occur sim-
ply because organizations don’t implement a patch management policy. As an example, 
Chapter 14 discusses several attacks on Equifax in 2017. The attack in May 2017 
exploited a vulnerability in an Apache Struts web application that could have been patched 
in March 2017. 
An effective
patch management
program ensures that systems are kept up-to-date 
with current patches. These are the common steps within an effective patch management 
program: 
Evaluate patches.
When vendors announce or release patches, administrators evaluate 
them to determine if they apply to their systems. For example, a patch released to fi x a 
vulnerability on a Unix system confi gured as a Domain Name System (DNS) server is not 
relevant for a server running DNS on Windows. Similarly, a patch released to fi x a feature 
running on a Windows system is not needed if the feature is not installed. 
Test patches.
Whenever possible, administrators test patches on an isolated nonproduc-
tion system to determine if the patch causes any unwanted side effects. The worst-case sce-
nario is that a system will no longer start after applying a patch. For example, patches have 
occasionally caused systems to begin an endless reboot cycle. They boot into a stop error, 
and keep trying to reboot to recover from the error. If testing shows this on a single system, 
it affects only one system. However, if an organization applies the patch to a thousand 
computers before testing it, it could have catastrophic results. 
Smaller organizations often choose not to evaluate, test, and approve 
patches but instead use an automatic method to approve and deploy the 
patches. Windows systems include Windows Update, which makes this 
easy. However, larger organizations usually take control of the process to 
prevent potential outages from updates.

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Managing Patches and Reducing Vulnerabilities