Step 4: Implementation

Zero Trust security policy focuses on creating allow lists because all breaches occur on allow rules. Focus on allowed traffic and allow only what you need.
The implementation phase of Zero Trust takes the assets you discovered and prioritized (step 1), your transactions (step 2), and your standards and designs (step 3), and translates those into:
  • User identity authentication and validation and device identity verification at all points of a transaction and whenever device posture, user behavior, or application behavior changes. No unknown users or devices (managed or unmanaged) should be in your enterprise.
  • Security policy rules that:
    • Create the architecture by segmenting the network, enforcing the principle of least privilege access, inspecting traffic, and logging traffic.
    • Adhere to your security standards.
    • Follow users everywhere in the enterprise.
  • Decryption policy rules that gain visibility into application traffic so that Security policy rules can inspect the traffic.
Security policy rules define a microperimeter for each asset and the segmentation gateway—a Palo Alto Networks physical, virtual, or cloud next-generation firewall—enforces the least privilege access defined in each policy rule. This enables you to control exactly who accesses each asset, how they access it, and when they access it. Secure each asset in a manner appropriate for that asset, following the principle of least privilege access. A microperimeter is easier to manage and defend than a broad perimeter that encloses different types of assets that have different purposes and access requirements. Microperimeters also move protections closer to critical assets.
Zero Trust Security policy consists of allow rules—rules that allow only authorized users to access specific resources using the specified applications at the right time in the right places. If traffic doesn’t match an allow rule, the firewall automatically blocks the traffic. This is important because:
  • It’s much easier to know the applications you want to allow to support your business than to take on the never-ending task of identifying and blocking all the applications you don’t want to allow.
  • All breaches and malicious activity happen on rules that allow. Focus security on traffic you allow and allow only the traffic required for business purposes.
When you plan Zero Trust policy implementation:
  1. Run the Best Practice Assessment (BPA) tool to set a best practice configuration baseline and see areas where you can improve security. As you develop and implement Zero Trust security policy rules, run the BPA periodically to measure progress.
  2. Think like a journalist about each asset or resource that you want to protect: who, what, when, where, why, and how should you allow access to the attack surface?
  • Who
    should access a resource?
    • User-ID identifies users and enables you to control who accesses a resource in policy. Through a lens of least-privilege access (who needs to know?), allow access only to individuals, groups, and devices that have legitimate business reasons to access a resource.
      Use the Cloud Identity Engine (CIE) to centralize cloud-based user and user group identification and user authentication. CIE aggregates all identity information across Identity and Access Management (IAM) solutions to provide consistent policy that follows users everywhere.
    • Create Authentication policy to verify the identities of users when they attempt to access resources. Authentication policy also determines whether to require Multi-Factor Authentication (MFA).
    • Use MFA to protect sensitive services and applications by requiring at least one more authentication factor in addition to entering a password in Authentication Portal, such as a one-time-use code delivered to a cell phone or email, before the firewall allows access to sensitive services, applications, and resources. For remote users, configure GlobalProtect to facilitate MFA notifications (you must also configure MFA on the firewall).
    • For devices that use GlobalProtect, configure Host Information Profiles (HIPs) to define access policy for hosts, enforce policy on those hosts, and prevent devices that don’t meet your security and maintenance standards from accessing resources. For example, you can use a HIP to ensure that endpoints have encryption enabled, the host’s antivirus signatures are up-to-date, etc. If a host doesn’t meet the HIP requirements, the security policy blocks access.
  • What
    application accesses the resource?
  • When
    do users access the resource?
    For applications that users access only during certain hours or at certain times of year (for example, applications used only for quarterly meetings), apply a schedule to the policy rule to prevent suspicious access during off-times. Adversaries often attack and attempt to exfiltrate data outside of normal business hours to reduce the chance of discovery. If an application used only at certain times of year or at certain times of day is used outside those times, that’s suspicious behavior.
  • Where
    is the resource located?
    Add the location of the destination resource to the policy. When appropriate, also restrict the source (zone and IP address) of the traffic.
  • Why
    is the data accessed—what is the data’s value if lost (toxicity)?
    Classify data to understand its toxicity—why is the data worth protecting? Would you have to disclose the loss if an attacker exfiltrated the data? Set up Data Filtering to prevent sensitive information from leaving your enterprise and use data classification tools to provide metadata about the data. Understanding the toxicity of data helps you determine how to protect data, what to do with data after using it, and how to tag it for use in policy.
  • How
    should you allow access to the resource?
    Apply Content-ID and best practices to protect against threats in application traffic:
    • Apply the philosophy of least-privilege access to security policy rules. Allow only users with legitimate business reasons to access only the applications they need to access for business purposes at only the proper times and only in the proper way.
    • Log all internal and external traffic through Layer 7. The firewall security policy rules enable logging by default. Forward logs to the Cortex Data Lake (or to Panorama or to Log Collectors) to consolidate logs for easier and more thorough analysis.
    • Apply policy and threat prevention consistently across all use cases (data center, cloud, branches, endpoints, etc.), for all local and remote users so the policy follows the user wherever the user goes, for all applications, and for all resources. Inconsistent policy increases vulnerabilities, is difficult to understand and maintain, and may negatively affect compliance requirements and audits.
      In addition to physical NGFWs and VM-Series, CN-Series, and cloud firewalls, use Prisma Access (cloud) and GlobalProtect (on-premise installation and with Prisma Access) to extend consistent Zero Trust policy to endpoints. For endpoints on which you don’t want to or can’t place an agent, use GlobalProtect Clientless VPN to apply consistent policy. Secure unmanaged IoT endpoints using the IoT Security service. Create and reuse Panorama templates and stacks to apply consistent policy across similar locations, such as your data centers or your perimeters.
    • Use cloud delivered security services (CDSS) whenever possible to ensure that you receive the latest threat prevention signatures in real time to protect against malware and command-and-control, advanced URL Filtering to control website access and prevent phishing attacks, WildFire for known and new malware, Enterprise DLP to prevent data exfiltration, SaaS Security to protect SaaS applications, IoT Security to protect unmanaged devices, and the DNS Security service to safeguard DNS transactions.
      Configure security profiles (Vulnerability Protection profiles for IPS, Antivirus and WildFire profiles to protect against malware including day-one malware, Anti-Spyware profiles to prevent command-and-control threats, File Blocking profiles to block or alert on risky file types, and URL Filtering to control website access, help prevent phishing attacks, and enforce safe search for search engines) and apply them to all allowed traffic. Follow best practices for data center firewall and perimeter firewall security profiles.
    • Use WildFire best practices to detect and prevent zero-day malware.
    • Use decryption best practices to decrypt as much traffic as regulations and business requirements enable you to decrypt so you can inspect as much traffic as possible. You can’t protect your enterprise against threats you can’t see.
    • Determine what to do with sensitive data after you use it—abstract it using encryption, tokenization, or masking, or dispose of it by archiving or deleting it. Archive stale data (approximately 80% of data on most systems hasn’t been accessed for two or more years).
    • Use Cortex XDR to refine and improve policy.
Understanding the who, what, when, where, why, and how of access enables you to create security policy rules that defend each asset appropriately because you understand who should have access, how they should have access, when they should have access, and the protections to apply. You can write business statements to develop Security policy rules, for example:
Who
What
When
Where
Why
How
Method
User-ID
CIE
IAM
App-ID
ACE
Time limits
System object
Classification
Content-ID
On-Premise
Epic_Users
Epic
Any
Epic_Srvr
Toxic (data has high value)
Decrypt, inspect (security profiles), log traffic
Cloud
Sales
Salesforce
Working hours
USA
Toxic (data has high value)
Decrypt, inspect (security profiles), log traffic
In both cases, the firewall allows only traffic that satisfies all of the conditions and passes inspection. The firewall automatically denies all traffic that doesn’t match an allow rule.
The Palo Alto Networks Zero Trust Advisory Service can help you design and implement your Zero Trust deployment.
In addition to security, authentication, and decryption policy, use DoS and Zone protection best practices to protect vital servers from denial-of-service (DoS) attacks.
For firewalls that you haven’t configured yet, use IronSkillet Day 1 configuration templates to implement a Day 1 best practice policy, then tune the policy to best suit your attack surfaces.

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