Principle of Least Privilege

Every permission you grant is a bet. A bet that the user won't make a mistake. A bet that their account won't get compromised. A bet that the application won't have a vulnerability. A bet that nothing will go wrong.

The principle of least privilege is about making fewer bets.

Grant only the minimum permissions necessary for each user, program, and system to perform its intended function. No more. This limits what can go wrong when—not if—something fails.

The Blast Radius Problem

When a security incident occurs, the damage depends entirely on what permissions were available.

A compromised user account with limited permissions gives attackers limited capabilities. They can access what that user could access—nothing more. A compromised account with administrative access gives attackers everything. They can disable security controls, destroy logs, move laterally through the network, and fully compromise the organization.

The difference isn't the sophistication of the attack. It's the permissions that were sitting there, waiting to be exploited.

This is the blast radius. Least privilege shrinks it.

Why We Over-Privilege

If least privilege is so obviously correct, why do we constantly violate it?

Because over-privileging is easier. Granting broad access "just in case" is faster than carefully analyzing what's actually needed. When someone requests access and you're not sure if they need it, saying yes avoids the conversation. When an application throws permission errors, granting admin rights makes the errors stop.

Every one of these shortcuts is a bet. Most of the time, you won't lose. But when you do lose—when that account gets compromised, when that application has a vulnerability—you lose big.

Users: Align Access with Responsibility

Role-based access control groups permissions into roles matching job functions. Finance staff get finance permissions. IT staff get IT permissions. Regular employees get user permissions. This is more manageable than individual assignments and ensures consistency.

Separate privileged accounts keep administrative capabilities isolated. Users have standard accounts for email, browsing, and routine work. When administrative tasks are needed, they switch to separate privileged accounts. Malware on the standard account can't reach administrative capabilities.

Just-in-time access provides elevation only when needed, for limited durations. Rather than permanent admin rights, users request temporary elevation for specific tasks. After approval, they get time-limited privileges that automatically expire. Even compromised admin credentials only work during approved windows.

Services: The Forgotten Attack Surface

Service accounts—accounts used by applications rather than humans—are where least privilege most often fails.

Services frequently run with excessive privileges because determining minimum requirements takes effort. It's easier to grant broad access and move on. But when that service gets compromised, attackers inherit those excessive privileges.

Identify minimum permissions for each service. What files must it read? Which database tables must it access? What network connections must it make? Grant only those specific permissions.

Use dedicated accounts for each service. Shared service accounts provide no isolation and muddy audit trails.

Rotate credentials regularly. Many organizations set service account passwords once and never change them. That credential has been sitting there, unchanged, for years—waiting.

Applications: Request Less

Applications should request only the permissions they actually need.

Mobile apps famously over-request. A flashlight app doesn't need access to contacts or location. Users are increasingly rejecting excessive permission requests—as they should.

Web applications often connect to databases with accounts that can do anything—SELECT, INSERT, UPDATE, DELETE, DROP, ALTER. If the application only reads from certain tables and writes to others, the database account should reflect exactly that. When SQL injection happens (and it does), the attacker can only do what the application could do.

Networks: Default Deny

Least privilege extends beyond permissions to network access.

Segmentation restricts which systems can communicate. Web servers need to reach database servers on specific ports. Database servers don't need to initiate connections to web servers. Firewall rules should reflect this.

Default deny blocks all traffic except explicitly permitted connections. Instead of blocking known-bad traffic, you permit only known-good traffic. Everything else fails.

Microsegmentation creates granular controls where each workload communicates only with the specific other workloads it needs. Lateral movement becomes difficult because there are no open paths to move through.

The Maintenance Reality

Least privilege isn't a one-time configuration. It requires ongoing work.

Permission audits regularly review who has access to what. Excessive permissions accumulate like clutter—they need periodic cleaning.

Access certification requires managers to periodically review and certify their team's access. "Does this person still need this access?" If no one asks the question, permissions only grow.

Anomaly detection identifies unusual permission usage. If an account suddenly accesses resources it never has before, something changed. Maybe it's legitimate. Maybe it's compromise.

The Challenges Are Real

Determining minimum permissions requires understanding exactly what each user or system needs. This is often unclear, especially for complex applications.

Legacy systems lack granular controls. You might only have "admin" or "user"—nothing in between.

User friction occurs when people can't do their jobs due to insufficient permissions. This generates complaints and encourages workarounds like credential sharing.

These challenges are real, but they're not reasons to abandon least privilege. They're reasons to implement it systematically:

• Start with role-based access that approximates least privilege
• Document permission requirements as you discover them
• Conduct regular access reviews
• Use privileged access management tools for temporary elevation
• Train users on why this matters

When Incidents Happen

The value of least privilege becomes viscerally clear during security incidents.

With least privilege in place: compromised accounts provide limited access, lateral movement is constrained by network segmentation, and forensics can trace exactly what was possible and what happened.

Without least privilege: a single compromised account can cascade into complete environment compromise. Attackers with administrative access can do anything—and often do.

The preparation you do before the incident determines the outcome during it.