What Is Zero Trust?
What Is Zero Trust?
Zero Trust is a security model that doesn’t trust a user, device, application, or workload just because it is inside the corporate network. In zero trust, every access is verified, limited and continuously monitored.
Older security models were built around the network perimeter where internal users and systems are trusted once they passed through the firewall or VPN. However, employees connect from different locations, business applications run across cloud and SaaS platforms, and service accounts or APIs often access data without a person signing in making such models less effective.
For zero trust, it evaluates whether a user, device, or workload should be allowed to access a specific resource under these conditions rather than checking if they are within the corporate network perimeter. This is verified based on identity, device status, requested resource, access behavior, session risk, and policy.
Why Perimeter-Based Security Is No Longer Enough
Perimeter-based security assumes the internal network as safe. This approach still helps in blocking unwanted traffic, but the main risk arises when an attacker gains access.
If attackers access the network through stolen credentials, session hijacking, or compromised devices, the behavior may appear to be legitimate to security controls. However, they can conduct lateral movement undetected while searching for file shares, admin tools, databases, and other accessible systems.
Cloud and SaaS adoption also weakens the perimeter-based security model. Data is distributed across collaboration tools, CRM platforms, code repositories, analytics systems, and cloud storage. A firewall around one office or data center cannot fully control how users, services, and workloads access those resources.
Zero Trust shifts protection closer to the resource. The goal is to reduce unnecessary access, verify context at each decision point, and limit the damage.
Core Principles of Zero Trust
Verify Explicitly
Explicit verification means every request from users and devices are verified before granting access. Users are verified through checking MFA, device security status, user role, location, time, requested application, and behavior.
For example, an employee may access the payroll system on a regular basis during business hours. However, if the same account tries to access the system at midnight from a different country, the request would be a signal of unusual activity. In this case, the account is valid, but the session is not.
Least Privilege Access
Least privilege means that the users and systems can access only the resources required for their role or task. Without least privilege, attackers will be able to access more systems and data increasing the impact of compromise.
This principle applies to all employees, administrators, contractors, service accounts, API keys, and automation tools. An account used by a user or application should not have access to databases that are unrelated to its use.
Least privilege also requires reviewing access regularly. Old permissions, unused accounts, legacy API keys, and temporary accounts should be removed once they can also become a major threat once compromised.
Assume Breach
Assuming breach is designing security based on the assumption that accounts, devices, or systems have already been compromised and limiting the movement within the system.
An infected account or device should not be able to reach the entire internal server and access sensitive data. In order to reduce risk, microsegmentation, limited permissions, session controls, and monitoring should be implemented.
Monitor Continuously
In Zero trust, users and devices need to be continuously monitored after verification, allowing security teams to understand what happens after access is granted.
Attackers often use legitimate credentials during attacks. The system should be able to terminate the session if a user shows abnormal behavior such as changing privileges, downloading large volumes of files, or triggering unusual API calls.
Key Components of Zero Trust Architecture
Zero trust architecture is architecture that combines the principles to systems, policies, and enforcement points. The key components of Zero Trust Architecture are identity, device, network, application and workload, data and polices
| Component | What It Covers | Security Check points |
|---|---|---|
| Identity | The human and non-human accounts that request access. Includes Users, administrators, contractors, service accounts, API clients, and automation tools. Each identity should be tied to a role and the permissions needed for that role. | IAM, SSO, MFA, privilege escalation, unusual logins and resource access. |
| Device | The devices used to request access. Includes laptops, desktops, mobile devices, servers, printers, and IoT systems. A valid user may still pose a potential risk if the device is unmanaged, outdated, or missing required security controls. | Patch and EDR status, disk encryption, certificate, jailbreak or rooting, managed device posture |
| Network | The network paths that connect users, workloads, and applications. Zero Trust limits these paths instead of treating the internal network as trusted. | Unnecessary internal paths, direct access from user devices to servers, workload-to-workload rules, lateral movement paths |
| Application and Workload | The applications, APIs, containers, serverless functions, and virtual machines that process business data. These resources should be accessed only through approved paths and required permissions. | API authentication, service account permissions, application call paths, exposed secrets in pipelines, abnormal runtime calls |
| Data | The sensitive information that users and systems access, store, move, or download. Access decisions should reflect the sensitivity of the data and the context of the request. | Sensitive data locations, access history, downloads, external transfers, unusual access volume, related identity activity |
| Policy Control | The policy layer that evaluates each access request and applies the decision at the point of access. It uses signals such as identity, device status, requested resource, risk level, and session behavior. | Access rules, session control, enforcement points, policy consistency. |
An access decision should not depend on identity. It should be decided based on device security status, the application that requests it, network path, data sensitivity, and session behavior. These signals help determine whether access should be allowed or denied.
Zero Trust Use Cases
Zero Trust can be applied in many cases as it changes how access is granted and reviewed. The following use cases show where the model can be applied.
Remote and Hybrid Work Access
In remote workplaces, employees need to access resources and business applications from outside the office. Zero trust can limit access instead of allowing broad internal network access.
A managed device may receive access to the requested resource, while an unmanaged device may require additional verification or have limited access. This reduces the possibility of opening the system to a stolen device.
Third-Party Access
Temporary access to internal systems is needed occasionally for partners and vendors. Zero trust limits access based on the user’s task, time and device conditions. Additionally, when the work ends, access is removed. This reduces the risk of old external accounts remaining active after the project has been completed.
Administrator Account Protection
Administrator accounts can create, delete, modify, and approve access across systems. Once attackers compromise the account, they can access critical systems causing sever damage.
Strict authentication can be applied through zero trust. Checking MFA, devices status, access time, session monitoring, and approvals can help reduce risk. The focus is not only who the admin is, but whether the action fits the context.
Cloud and SaaS Application Security
Business data often lives across email, collaboration tools, CRM systems, cloud storage, and developer platforms. Zero Trust applies access controls at the application and data layer, not only at the network layer. If a normal login is followed by mass downloads, unusual API calls, or unusual access to sensitive data, security teams need to review the activity with identity and device context.
Containing Ransomware Through Access Control
Ransomware attackers move from the compromised endpoint to file servers, backup systems, and admin tools.
Zero trust uses least privilege and microsegmentation to reduce paths used for lateral movement. It keeps the communication path closed unless it is needed. The goal is to limit spread even when a system is compromised.
Developer and CI/CD Pipeline Security
Development environments connect source code, build systems, deployment tools and cloud credentials. Zero Trust treats developers, automation tools, build systems, and service accounts as access subjects. Code repository access, deployment permissions, secret usage, and API keys should be scoped and monitored.
Sensitive Data Access Control
Sensitive data includes customer records, credentials, source code, financial data, contracts, and internal business plans. In zero trust, access control should apply not only to developers but also to build systems, automation tools, and service accounts. Access to the system can be limited to what the user or system needs.
How to Implement Zero Trust
Zero Trust should start with visibility, not tool selection. Security teams need to know what they are protecting, who can access it, and which access paths create the most risk.
A practical starting point is to identify sensitive data and critical systems such as customer data, identity platforms, admin consoles, code repositories, production systems, and cloud management accounts.
The next step is to review identities and permissions. Dormant accounts, shared accounts, broad admin rights, unused service accounts, old API keys, and unmanaged third-party access should be removed.
Access policies can then become more specific. Security teams can define access by user role, device status, application sensitivity, location, time, and session behavior. Starting with monitoring policies helps avoid business disruption.
Response workflows also matter. If a risky session is detected, the team should be able to terminate the session, revoke access, isolate the device, require reauthentication, or open an investigation. Detection without action leaves the risk active.
Limits and Common Mistakes
Implementing zero trust does not mean the system is safe. Poorly planned Zero Trust programs can add friction without reducing meaningful risk.
One common mistake is adding new tools without the process of mapping assets, identities, and access paths. Without such context, policies can disrupt normal work while leaving high-risk accounts untouched.
Another mistake is considering zero trust as fully implemented with only MFA. MFA is important, but attackers can steal session tokens, use approved devices, or abuse overprivileged service accounts. Identity must be evaluated with device, behavior, application, and data context.
Zero Trust also requires operational discipline. Permissions must be reviewed, exceptions must expire, policies must be tested, and alerts must connect to response actions. Otherwise, the environment may still depend on old trust assumptions under a new label.
FAQ
What does Zero Trust mean?
Zero Trust means no user, device, application, or workload is trusted automatically. Each access request is verified using identity, device, resource, behavior, and policy context.
Is Zero Trust a product?
No. Zero Trust is a security model and operating approach. Products such as IAM, MFA, ZTNA, EDR, SIEM, CNAPP, and data security tools may support it, but no single product completes Zero Trust by itself.
What is the difference between Zero Trust and ZTNA?
ZTNA is a remote access method based on Zero Trust principles. Zero Trust is broader. It covers identity, devices, networks, applications, workloads, data, policy enforcement, and monitoring.
Does Zero Trust replace VPN?
In some environments, ZTNA may replace parts of VPN-based access. In other environments, VPN may remain for specific use cases. The main goal is to avoid broad network access when users only need specific applications.
Why is least privilege important in Zero Trust?
Least privilege limits what users and systems can access. If an account is compromised, narrow permissions reduce the number of systems and data sources the attacker can reach.
Where should a Zero Trust project begin?
A practical starting point is to identify critical systems and sensitive data, then map who and what can access them. From there, teams can remove unnecessary permissions and apply stronger verification to high-risk access.
Our Zero Trust Implementation Strategy
We supports zero trust implementation based on our network security solution, AhnLab XTG. By integrating AhnLab XTG's ZTNA(Zero Trust Network Access) capabilities with endpoint security and threat intelligence platforms, we provide an integrated zero trust security framework. This enables verification of the security posture of users and devices, allowing access only to verified users and applying core Zero Trust principles.