What is the principle of least privilege? The risks of excessive privileges and specific steps for designing IAM.

Even though we're told that the "principle of least privilege" is important, many people don't know how to actually design things in AWS. This is where many projects get stuck.

Prioritizing business continuity by granting administrator privileges and addressing problems later is a flawed approach. As long as this practice continues, privileges will continue to increase and eventually become uncontrollable. The risks of information leaks and user errors arise from neglecting such excessive privileges. The principle of least privilege is not merely a security principle. It only functions effectively when designed with IAM policies and roles in mind, including the use of temporary credentials and an operational approach that anticipates review and adjustments.

This article outlines the fundamental concept of least privilege, the structural problems that prevent its implementation in practice, and key design and operational points based on AWS IAM. It clarifies the criteria for avoiding excessive privileges while addressing common points of confusion in real-world applications.

What is the principle of least authority?

The principle of least privilege is widely known as a fundamental aspect of security. However, in practice, it is not often correctly designed and implemented.

While the explanation "granting only the minimum necessary authority" is easy to understand, it's an area where it's easy to become ambiguous about what constitutes "necessary" authority. As a result, authority expands in order to prioritize work, and before you know it, the situation becomes uncontrollable. This kind of discrepancy is occurring in many workplaces.

In AWS, the principle of least privilege is organized around the idea of ​​"allowing only the necessary actions on specific resources under specific conditions." It's not simply about reducing permissions, but rather a design issue that specifies who is allowed what and to what extent, in line with business operations.

The principle of least authority is not merely a concept; it's a matter of design and implementation. If this is misunderstood, it won't function even if the form is correct.

Definitions and Basic Concepts (PoLP)

The principle of least privilege (PoLP) is based on the idea of ​​granting users and systems only the privileges necessary for their work. Unnecessary operations and access to resources are not permitted.

The key is to use the "minimum" level of granularity. Instead of simply reducing permissions, you need to break down the operations required for each task and limit them to that scope. If this is unclear, you may think you are restricting permissions, but in reality, you are granting broad permissions.

Even with AWS IAM, access permissions are not granted by default; it's assumed that you explicitly grant the necessary permissions. That's why a design that breaks down and builds up the necessary operations is more logical than "granting broad permissions initially and then restricting them later."

This applies not only to users, but to all entities, including applications, batch processing, and external service integrations. In particular, in the cloud, it is recommended to design not only people but also workloads based on roles and temporary authentication credentials, and permission design must include consideration of inter-system integrations.

Why is it important now? (Cloud Zero Trust)

In traditional on-premises environments, the focus was primarily on controlling access both inside and outside the network. A design that allowed for a certain degree of flexibility within the internal network was often sufficient.

In the cloud, this premise changes. Instead of focusing on the network, the key becomes who can access which resources and to what extent. Access control revolves around identity and permissions. Even in AWS, the best practice is to manage user access by having individuals assume roles through IAM Identity Center or federation, and using temporary credentials.

The zero-trust approach aligns with this principle: do not trust anyone, even internally, and verify all access based on the assumption that it is legitimate. Under this premise, excessive privileges become a risk. If authentication is breached, the entire scope of those privileges becomes a target for attack. The combination of least privilege and temporary credentials is crucial in minimizing these risks.

The principle of least privilege is a fundamental design element in such environments. It's something that should be incorporated from the start, rather than being an add-on later.

The misconception that "the more authority you have, the safer you are."

In the workplace, it's sometimes considered safer to grant broader authority. The intention is to avoid the risk of work being halted due to insufficient authority.

While this may seem rational in the short term, this decision will create problems in the long run. Having broad authority means having many options, but also a wide range of influence. If errors, configuration mistakes, or account misuse occur, the impact will extend to the entire system.

Permissions, once granted, are difficult to revert. Permissions added for business purposes accumulate, making it difficult to grasp the overall picture. As a result, the system approaches a state of uncontrollability. AWS also recommends granting least privileges, limiting them to specific actions, resources, and conditions, and normalizing broad privileges goes against this principle.

The principle of least privilege is not meant to be inconvenient. It's designed to limit the scope of impact and minimize damage when problems occur.

What happens when the principle of least privilege is not followed?

In environments where the principle of least privilege is not in effect, the scope of impact when a problem occurs cannot be controlled. Even if individual operations seem minor, depending on the breadth of privileges, they can have repercussions throughout the entire system.

Excessive privileges are often difficult to notice during normal times, but they become apparent all at once when a problem occurs. Incidents aren't always caused by special attacks; most occur as an extension of routine operations. Even in AWS's philosophy, a situation where the principle of least privilege isn't followed leads to a structure that easily spreads the scope of damage.

Typical accident patterns caused by excessive authority

A common problem is accidental actions caused by accounts with excessive privileges. Tasks that should only require limited changes can end up affecting other resources due to broader permissions.

For example, there are cases where a setting change intended for the development environment is applied to the production environment as a result. Or, cases where important data is unintentionally deleted. In both cases, the operation itself is not special.

Another concern is the leakage of authentication information. If access keys or session information are leaked externally, they can be used to manipulate the system within the scope of those permissions. The damage will be particularly significant if long-term access keys are used with broad permissions. AWS also recommends prioritizing temporary authentication information provided by roles over the regular use of long-term access keys for IAM users.

Lateral movement of authority

After an attacker acquires one account, they may then expand their access to other resources. This is known as lateral movement.

In environments with excessive privileges, this lateral movement becomes easier. If a single account is granted access to multiple services or resources, it can then easily infiltrate other areas. AWS best practices also treat least privilege as a prerequisite for mitigating the risks of lateral movement and privilege escalation.

Ideally, permissions should be separated by business function. However, in practice, permissions are often consolidated for the sake of "convenience," resulting in an increase in the number of entry points for intrusions.

A structure where "one person's mistake" can lead to a whole-party disaster.

In a state of excessive authority, individual actions directly affect the entire system because there is no systemic safeguard.

For example, if all operational permissions are centralized under a single administrator account, any mistake or misuse in that account will immediately spread to the entire system. There is no mechanism to limit the scope of the impact.

The problem lies in the fact that these structures are created unintentionally. Expanding authority to facilitate operations leads to a situation that is increasingly out of control. By the time it's noticed, no one can explain the extent of the impact.

The principle of least privilege is designed to break this chain reaction. It limits the scope of impact in advance and localizes the damage when a problem occurs. This design directly relates to AWS's concept of "keeping the scope of impact small."

The real reason why least privilege cannot be achieved

Despite the understanding of the importance of least authority, it doesn't function effectively in many workplaces.

The cause is not a lack of technical skill, but rather a problem with the design and operational assumptions.

Permissions should be defined from the beginning, not added later. If this is left ambiguous, the accumulation of exception handling will make it impossible to control the system.

The authorization system is being designed without clearly defining the business requirements.

Designing the principle of least privilege requires specifically breaking down "who," "why," and "what operations" are performed. If this breakdown is insufficient before designing the privileges, it will be impossible to define the necessary scope.

As a result, a broad range of permissions is granted based on a vague sense of "this much should be necessary." Permissions are added every time the work changes, while unnecessary ones remain. The initial ambiguity simply accumulates.

The culture of escaping by saying, "Just give me administrator privileges."

To avoid work being halted due to insufficient permissions, it's common practice to grant strong permissions from the start. This decision is often prioritized, especially during initial setup and troubleshooting.

It's efficient in the short term. However, if that situation becomes the norm, you lose the opportunity to review it. What was originally meant to be a temporary solution becomes a permanent operation. As a result, you lose track of which accounts have what level of control.

Permissions continue to increase during operation (permission creep)

Permissions are added, but rarely removed. Permissions granted each time there are changes to business processes or exceptions remain in place.

Over time, authority levels become more complex, making it impossible for anyone to grasp the overall picture. In this state, even identifying unnecessary permissions becomes difficult. As a result, excessive authority becomes the norm.

Fragmentation of development, operations, and security

Access control design is not something that can be completed by a single team alone. Development prioritizes feature implementation, operations focus on stable operation, and security demands risk reduction. If each perspective remains fragmented, a consistent design cannot be achieved.

The development team implements the system with broad permissions, and the operations team simply adopts those permissions. The security team tries to impose restrictions afterward, but the impact on business operations is so significant that they cannot adjust the settings. This cycle repeats itself.

The inability to implement the principle of least authority is not a matter of individual judgment; it stems from a lack of proper design, operation, and organizational premises.

Design steps to achieve least privilege

The principle of least privilege cannot be achieved simply by writing detailed policies. It requires designing a series of processes, starting with breaking down business processes, granting privileges, controlling them, and reviewing them.

In AWS, the principle of least privilege is to grant only the necessary permissions for the tasks that are required. The key is not to increase the number of settings, but to design the permission boundaries from the start. Here, we'll outline the basic steps to implement this in a way that works in practice.

STEP 1: Break down the necessary permissions into individual business units.

The first thing to do is not to assign authority, but to organize the tasks. Break down the tasks specifically, determining who is responsible for which tasks and what operations are required within those tasks.

Instead of using abstract definitions like "managing servers," we break it down to operational levels such as "starting an instance" and "checking logs." Unless we break it down this far, the scope of necessary permissions won't become clear.

Skipping this step will make all subsequent design work ambiguous.

STEP 2: Organize by role (RBAC)

If we directly link the broken-down tasks and operations to individuals, it becomes impossible to manage them. Therefore, we group permissions by role and organize them as roles.

Members performing the same tasks are assigned the same role. This ensures operational stability, as roles can be changed upon transfers or departures. In AWS, the basic approach is to define different policies and assign permissions for each job function.

The important thing is not to create roles that are too granular. If the granularity is too fine, management will break down, and you will end up going back to granting permissions to all users at once.

In environments where multiple teams handle different resources within the same account, it may be easier to manage if you combine ABAC (Account-Based Access Control) with RBAC (Account-Based Access Control) which uses tags and attributes for control, rather than just RBAC.

STEP 3: Design with the assumption of "default rejection".

The principle of least privilege is based on the idea that "all operations that are not permitted are denied." Only necessary operations are explicitly permitted, and all others are denied.

Conversely, a design that "grants broad permission and then removes unnecessary features" cannot be controlled. Any omissions in the removal process will directly result in excessive authority.

The key is to limit the scope of permissions from the very beginning. This order is crucial. Even in AWS, the principle of least privilege is based on granting only the necessary actions with the necessary conditions.

STEP 4: Decide how to handle exception access.

Operating everything with minimum privileges inevitably leads to exceptions. These are situations where broader privileges are needed, such as for emergency responses or temporary tasks.

If you grant the authority permanently at this point, the design will break down. You need to include a mechanism in the design beforehand to "temporarily grant the authority and then revert it after the work is done."

In AWS, temporary credentials form the basis of roles and federation, and can be treated as permissions with expiration dates. Whether for human access or workloads, it is safer to adopt this approach than to use long-term credentials on a regular basis.

STEP 5: Assume logging and auditing are necessary.

Permissions aren't a one-time design; you need to understand what operations are actually being performed and continuously review them.

The system is designed based on access logs and operation history, enabling the detection of "unused permissions" and "unexpected operations." This entire process is considered minimum permission.

AWS allows you to record IAM and STS API calls with CloudTrail. In addition, using IAM Access Analyzer makes it easier to find clues about unintended exposures, sharing, and permission reviews.

Without an auditing mechanism, authority will continue to increase. It is essential to incorporate a review mechanism from the design stage.

Implementing least privilege in AWS (IAM design)

When implementing least privilege in AWS, the core of the process lies in IAM design. Defining which operations are permitted, for which resources, and under what conditions, directly defines the security boundary. Even in AWS, the principle of least privilege is to grant only the necessary permissions for necessary tasks.

The key is not to write a policy, but to clearly define "what is permitted." If you write it vaguely, you will unintentionally end up with broad permissions. In addition, when it comes to human access, it is easier to maintain least privileges if you design it based on roles and temporary credentials rather than directly building permissions up for IAM users.

Basics of IAM policy design

An IAM policy consists of a combination of the operations to be allowed, the resources to be targeted, and the conditions under which they are allowed.

• Action: Which operations are allowed?
• Resource: Which resource is being operated on?
• Condition: Under what conditions will it be permitted?

Only when these three elements are present can the scope of permissions be clearly defined. In AWS, the principle of least privilege is to allow specific actions on specific resources under specific conditions.

A common problem in many designs is the omission of Resource and Condition. Specifying only Action can easily lead to a broader scope of actions, potentially resulting in unintended manipulation of resources.

However, there are some points to note. Not all AWS actions support resource-level permissions or condition keys. You will need to consult the Service Authorization Reference for each service to determine how finely you can restrict permissions.

Design principles that avoid using the asterisk (*)

A common mistake in IAM design is relying on wildcards. Allowing all resources and all operations at once defeats the purpose of the design.

While convenient in the short term, it obscures the extent of your control. As a result, you lose control over the scope of the impact.

The basics are to clearly specify the target resources and limit operations to only those that are necessary. Simply adhering to these two points will significantly limit the scope of permissions. However, in AWS practice, the goal is not to "never use wildcards." It is important to start with the bare minimum and narrow it down to the scope of Action, Resource, and Condition that each service supports.

Pitfalls of managed policies

AWS-provided managed policies can sometimes result in excessive privileges if used as is.

Many AWS Managed Policies are designed to be broad and general-purpose. Therefore, they often include permissions that are unnecessary for specific tasks.

Applying it as is will unintentionally enable a wide range of operations. It's important to note that AWS managed policies cannot be edited. If you want to limit permissions to only what you need, you need to create a customer managed policy and define only the necessary permissions, rather than directly modifying the AWS managed policy.

Differentiating between roles and users

IAM offers two ways to grant permissions: directly to users and through roles. From the perspective of least privilege, a role-centric design is fundamental.

Using roles allows you to link permissions to roles rather than individuals. This makes it easier to centrally manage the granting, changing, and deleting of permissions.

On the other hand, directly granting permissions to users increases the amount of individual management required, making it difficult to see the overall picture. As a result, excessive permissions and failure to delete permissions become more likely. AWS also recommends using temporary credentials by assuming IAM roles through IAM Identity Center or federation, rather than keeping long-term credentials attached to IAM users for human access.

Utilization of temporary permissions (STS / AssumeRole)

Designing a system to grant strong privileges at all times contradicts the principle of least privilege. A mechanism is needed to grant privileges only when necessary and then revert them after the task is completed.

AWS allows you to grant temporary permissions using STS or AssumeRole. Temporary credentials are the foundation of roles and federation, and because they have an expiration date, they don't remain around for long after you're done using them.

Normally, users operate with limited permissions, only assuming roles when necessary. This mechanism allows you to meet business requirements while keeping permissions to a minimum at all times. Furthermore, using IAM Access Analyzer's policy validation when creating or reviewing policies makes it easier to identify overly broad permissions or problems with the policy description in advance.

Common failure patterns and anti-patterns

While the principle of least authority clearly defines what needs to be done, the ways in which failures can occur are also somewhat predictable.

The troublesome thing is that many of these decisions stem from what appears to be rational judgments in the field.

Prioritizing immediate efficiency can result in structures that are difficult to modify later. The following are typical patterns that are frequently repeated in practical work.

Designed to allow for the removal of full access later.

While initially granting broad permissions and later removing unnecessary ones may seem practical, this method rarely results in achieving the principle of least privilege.

To identify which permissions should be removed, you need to understand which operations are truly necessary. However, without a clear overall picture of the business processes, it's impossible to make such decisions, and the reduction process won't progress.

As a result, the "review later" step is postponed, and a near-full access state is maintained. If the design order is reversed, it becomes more prone to failure at that point.

The test environment and production environment have the same permissions.

Sometimes, due to prioritizing development and testing, the same permissions as in production are granted to the test environment. Alternatively, these permissions may be directly transferred to production.

In this state, testing operations could potentially affect the production environment. Permission boundaries disappear, and errors or configuration mistakes are directly reflected in the production environment.

While separating permissions for each environment is fundamental, it's a point that's often omitted for operational convenience.

I haven't looked at the audit logs.

Although logs are being collected, they are not actually being reviewed. In this state, the validity of the permission design cannot be verified.

Without understanding which operations are being used and whether any unexpected access is occurring, it's impossible to decide whether to remove unnecessary permissions. Even if AWS allows you to track operation history with CloudTrail, it's meaningless if you don't use that data for review.

As a result, permissions continue to increase. Logs only become meaningful when you look at them, not when you collect them.

Authority design is dependent on individual users.

Only certain individuals understand the authority structure. In this situation, the design intent is not shared, and consistency breaks down with every change.

When the person in charge changes, permissions are added without a thorough understanding of the existing design. As a result, it becomes impossible to explain which permissions exist and why.

The principle of least authority cannot be maintained solely through individual skills. It requires clearly defined design intents and rules, and management within the organization.

Key points for maintaining minimum privileges in operations

The principle of least privilege isn't something you design once and forget about. From the moment operations begin, privileges continue to change. When tasks are added, personnel changes occur, and exceptions are handled, the assumptions made during the design phase quickly break down. Therefore, what's needed is an operation that takes into account the expected increase in privileges and periodically reviews and restores them. Even in AWS, least privilege is treated as something that should be continuously managed and improved.

Regular authority review

This process involves reviewing whether the permissions currently granted are truly necessary. Unless this is done regularly, unnecessary permissions will persist.

The key is not to just look at the list and be done with it. You need to compare it with your actual work, identify the permissions you're not using and the permissions that don't match your role, and decide which ones to keep and which to remove.

The value of inventory lies not in simply understanding the current situation, but in removing unnecessary authority and restoring the design to its original state.

Automatic detection of unnecessary permissions

Manually checking everything is not practical. Therefore, we incorporate an automated detection mechanism.

AWS allows you to use IAM Access Analyzer to detect unused access, validate policies, and generate policies based on CloudTrail logs. These features help reduce oversights and make it easier to prioritize where to start reviewing your policies.

However, the tool doesn't take over the decision-making process. How to handle the detected results ultimately depends on business requirements and operational policies.

Development of an authorization request flow

Leaving the addition of permissions to individual discretion will lead to a buildup of exceptions. It's essential to clearly define who requests what permissions, for what reason, and within what scope.

If approval criteria remain vague, it becomes easier to grant broader authority. By linking the criteria to business requirements, it becomes easier to prevent excessive authorization.

The purpose of streamlining the workflow is not to increase the number of procedures. It is to prevent decisions regarding the granting of authority from being left to individual experience or intuition.

A system for "temporary granting → automatic revocation"

Situations requiring exceptionally strong authority are unavoidable. The problem is that this authority persists even after the work is completed.

The solution is clear. We will design it to grant the benefit temporarily and then automatically revoke it after a certain period of time. Manual revocation will inevitably lead to errors.

In AWS, temporary credentials are issued by the Security Token Service (STS) and are valid for a limited time. Whether for user access or workloads, it's easier to maintain least privileges by only assuming roles when needed, rather than maintaining long-term credentials.

Instead of always granting strong privileges, grant them only when necessary. Whether or not you can maintain this balance significantly impacts the application of the principle of least privilege.

The relationship between least privilege and zero trust

Least privilege and zero trust are often discussed as separate concepts. However, the underlying idea is the same. Both require a design that controls access on a case-by-case basis, rather than the idea of ​​"trusting access once it's granted."

Instead of judging security based on whether it's inside or outside the network, the scope of permission is defined on an access-by-access basis. The principle of least privilege is to determine what is permitted and to what extent. This concept is essential for zero trust to work.

Why is PoLP a prerequisite for zero trust?

Zero Trust verifies all access. It checks authentication and device status before deciding whether to grant access.

The crucial point here is determining how far you will allow operations after authentication. If you grant broad privileges simply after successful authentication, risks remain at that point.

If the principle of least privilege is in effect, even if authentication is breached, the scope of impact will be limited. Conversely, in a state of excessive privilege, even if zero trust is implemented, the damage cannot be adequately mitigated.

If zero trust is about control at the entry point, then least privilege is about control further down the line. Neither one alone is sufficient.

Why IAM is central to security

In a cloud environment, access control shifts from the network to IAM (Independent Management Interface). The definition of who can perform which operations on which resources becomes the very boundary of security.

Network control alone cannot finely restrict operations after gaining access to the network. On the other hand, IAM allows you to separate permissions and denials on an operation-by-operation basis.

Therefore, the focus of security design shifts to IAM. The extent of the impact will depend on how strictly the principle of least privilege can be designed.

In achieving zero trust, IAM is not merely a configuration item; it is a design element that underpins the entire system.

Summary

The principle of least authority is not simply about reducing authority. It's about defining who is authorized to do what and to what extent on a business unit basis, and maintaining that definition in both design and operation.

The reason why these systems tend to become mere formalities in practice is not so much a technical issue, but rather due to ambiguity in business requirements, a culture of proceeding with "administrator privileges for now," and the accumulation of exception handling. Ambiguities that were not properly addressed during the design phase remain as excessive privileges during operation.

In AWS, the implementation of least privilege is directly tied to how you design IAM policies, roles, and temporary permission granting mechanisms. Furthermore, it cannot be maintained without incorporating mechanisms for regular inventory checks, log review, and automated detection.

The principle of least privilege is also a prerequisite for zero trust and cloud security. This is because even strong authentication is meaningless if the privileges granted after authentication are too broad. The important thing is not to treat least privilege as a "configuration item." It only functions effectively in practice when viewed as a single system encompassing design, exception handling, and auditing.