A service principal is an identity created for software rather than for a person. When an application, a script, a deployment pipeline, or an automation tool needs to sign in to a cloud environment and do something, it does so as a service principal. It has a name, an ID, a set of credentials it uses to prove who it is, and a set of permissions that define what it is allowed to do.
The term is most closely tied to Microsoft Entra ID (formerly Azure Active Directory), where “service principal” is the official name for this kind of identity. The same idea exists in every cloud under different names: IAM roles on AWS and service accounts on Google Cloud. If you understand service principals, you understand the pattern behind all of them.
This matters for security because service principals are everywhere, they are powerful, and they are far less closely watched than human accounts. When attackers steal a secret from public code, they very often steal the credentials of a service principal. This guide explains what one is, how it differs from an app registration, how it signs in, where the risks come from, and how to manage it safely. It assumes no prior knowledge of Entra.
Why software needs its own identity
Start with a person. When you sign in to the cloud, you prove who you are with a password and a second factor such as an app prompt or a security key. The system then knows you are you, and checks what you are allowed to do.
Software cannot do that. A nightly backup job does not have a phone to approve a prompt. A deployment pipeline cannot type a password. Yet both need to act in your cloud: read a database, push an image, change a setting. So the cloud gives the software its own identity, with its own credentials and its own permissions, separate from any human. That identity is the service principal.
This separation is intentional. You do not want an application running on a developer’s personal login, because if that person leaves or is compromised, the application breaks or the attacker gains the application’s access. A dedicated identity lets you grant just what the application needs and remove it when the application is retired.
App registration vs service principal (the part that confuses people)
In Entra you will see two related objects, and mixing them up is the most common source of confusion.
- App registration (the application object). This is the definition, or blueprint, of an application. It describes what the app is: its name, the permissions it can request, how it signs in. It lives in one place, the tenant where the app was registered. Think of it as the design.
- Service principal. This is the instance of that application inside a specific tenant. It is the actual identity that holds role assignments and permissions there. It is what signs in and what gets access to resources. Think of it as the badge issued from the design.
Microsoft documents the relationship in application and service principal objects. When you register an app in your own tenant, a service principal is typically created alongside it. When an app from another organization is given access to your tenant, a service principal is created in your tenant that points back to the app’s definition elsewhere. That is how multi-tenant software, including many SaaS integrations, gets access to your environment.
The practical takeaway: permissions and access live on the service principal. When you audit who can do what in your cloud, you are looking at service principals and their role assignments, not at the app registration.
The types of service principal
Microsoft describes several kinds, and it helps to know the two you will meet most often.
- Application service principal. Created from an app registration. It can sign in using credentials you manage: a client secret or a certificate.
- Managed identity. A special service principal that Azure creates and manages for you, attached to an Azure resource such as a virtual machine, function, or container app. There is no secret to store or rotate. The platform handles the credentials. Managed identities come in two flavors: system-assigned (tied to one resource’s lifecycle) and user-assigned (a standalone identity you can attach to several resources). See the Microsoft overview of managed identities.
Managed identities are the safer choice wherever they are available, because there is no secret to leak. Application service principals with client secrets are where most of the risk lives.
How a service principal signs in
A service principal proves its identity with a credential. There are three main kinds:
- Client secret. A password-like string generated for the app. Easy to create and use, which is exactly the problem: it is a static value that can be copied, committed to code, logged, or sent in chat. It works from anywhere until it expires or is removed.
- Certificate. A key pair, where the private key proves identity. Stronger than a secret in principle, but the private key still has to be stored somewhere and can be stolen like any other file.
- Federated credential. No stored secret at all. The service principal trusts a token issued by another system, for example a CI/CD platform, and exchanges it for a short-lived cloud token. See workload identity federation. This is the preferred approach for pipelines.
Once the service principal presents its credential, Entra checks it and returns an access token. The token is what the app then shows to cloud services to prove it is allowed in. Tokens are short-lived, but the credential that obtains new ones is not, which is why protecting the credential is the central task.
A key difference from human accounts: service principals do not do multi-factor authentication. There is no second factor to prompt. Whoever holds the credential can sign in as the service principal, from any location, at any time. The credential is the whole defense.
The same idea in other clouds
| Concept | Microsoft Entra / Azure | AWS | Google Cloud |
|---|---|---|---|
| Identity for software | Service principal | IAM role (and, less ideally, IAM user) | Service account |
| Platform-managed, no secret | Managed identity | IAM role attached to compute | Attached service account |
| Static secret to avoid | Client secret | Long-lived access key | Service account key file |
| Secretless from CI/CD | Workload identity federation | OIDC role assumption | Workload identity federation |
Google documents these in service account overview and its own workload identity federation. AWS describes its model in IAM roles. The terminology changes, but the risk pattern does not: an identity for software, a credential, and a set of permissions.
Why service principals are such an attractive target
Several properties combine to make them a favorite of attackers.
- They often hold broad permissions. To avoid errors, teams grant a service principal generous roles at a wide scope, such as Contributor across a whole subscription. Nobody wants a deployment to fail at 2 a.m. The breadth stays long after it is needed.
- Their credentials are static and long-lived. A client secret can be valid for months or years. A Google service account key file does not expire by default. A secret leaked today can be used long afterward.
- They bypass the controls that protect people. No MFA, no push prompt, no “unusual sign-in, was this you?” step in many setups.
- Nobody owns them. The developer who created one moves on. The app is retired but the service principal remains. No one is responsible for reviewing it.
- They are numerous and invisible. A mid-sized cloud estate can have thousands. Few teams have a complete list, let alone a review process.
- They are easy to leak. Secrets get pasted into code, build logs, tickets, and chats. This feeds directly into secrets sprawl.
A recent example of the result: automated tools scanning public GitHub for exposed secrets, then using a found service principal secret to sign in and reach a key vault within minutes. We cover that incident in AI agents scanning GitHub for secrets and reaching Azure Key Vault. The attacker never needed to break anything. They used a real credential.
How service principals get abused
Knowing the typical sequence helps you spot it.
- Obtain the credential. From public code, a leaked log, a compromised developer machine, or a third party.
- Sign in as the service principal. This looks like normal automation activity, because it is the same identity.
- Explore. List what the identity can reach: subscriptions, resource groups, key vaults, storage.
- Escalate or persist. Add a new secret to the same service principal, create a new one, or assign themselves roles, so access survives even if the original secret is rotated.
- Take data or use resources. Read secrets from a key vault, copy data from storage, or run compute at the victim’s expense.
Step 4 is the one that catches people out. Rotating a leaked secret does not help if the attacker has already added their own. This is part of the case for proper rotation and revocation.
How to secure service principals
1. Make an inventory and give every one an owner
List every service principal, what it is used for, who owns it, what permissions it holds, which credentials it has, and when each credential was last used. A service principal with no owner and no recent activity is a candidate for removal.
2. Prefer secretless authentication
Use managed identities for workloads running inside the cloud. Use federated credentials for pipelines instead of storing a secret in CI/CD variables. Every secret you remove is a secret that cannot leak.
3. Apply least privilege
Grant the narrowest role at the narrowest scope that still works. Avoid broad built-in roles such as Owner and Contributor at subscription level for automation. Review permissions regularly, and remove those that are never used. CIEM automates this by comparing granted permissions with actual use.
4. Where secrets are unavoidable, keep them short-lived and rotate them
Set short expiry dates. Prefer certificates over secrets where practical. Store credentials in a vault, never in code or config files. Have a rotation process that is tested and routine. See what is secret rotation.
5. Restrict where they can sign in from
Conditional Access policies for workload identities can limit a service principal to expected locations. Microsoft offers this as part of its workload identity licensing, so check what your tier includes. Even without it, network restrictions on the resources themselves help.
6. Control who can create credentials
If anyone with a certain role can add a new secret to any application, an attacker with that role has a persistence mechanism. Restrict and monitor who can manage app credentials and role assignments.
7. Monitor service principal activity
Entra records service principal sign-ins separately from user sign-ins. Alert on a service principal signing in from a new location, using a credential that has been dormant, performing actions it has never performed, or having new credentials added.
8. Remove what you do not use
Delete service principals for retired applications. Remove expired or unused credentials. Offboard them the way you offboard people.
How service principals relate to other concepts
A service principal is one kind of non-human identity, the broad category that also includes API keys, bots, and AI agents. It is a primary subject of CIEM and a core part of IAM in the cloud. Its permissions define the blast radius of a stolen credential, and the goal of zero standing privilege applies to service principals just as it does to people.
How Cloudanix helps
Cloudanix does not replace Entra ID or change how service principals authenticate. It gives you visibility into them, helps reduce their permissions, and reduces how long their access stands open.
- See every identity. The unified asset graph covers identities across AWS, Azure, and GCP, including service principals, roles, and service accounts, so you can answer “which non-human identities exist and what can they reach?” in one place. See non-human identity security.
- Find over-permissioned and unused access. CIEM highlights entitlements that are granted but never used, so permissions can be cut back.
- See how far a stolen identity reaches. Attack path analysis maps what a compromised service principal could access, including vaults and data stores.
- Find leaked secrets. Code Security scans for exposed credentials, including cloud and service principal secrets, using 2,000+ patterns.
- Replace standing access with short-lived access. Agentic JIT and Cloud JIT provide scoped, time-limited access for pipelines, automation and people, so there is less permanent access for a thief to inherit.
- Detect unusual behaviour. Cloud UEBA and cloud detection and response flag identities acting out of character.
As always, there are limits. Cloudanix reads from the accounts and tenants you connect, so a service principal in an unconnected tenant will not appear. And secretless authentication has to be adopted in your pipelines and applications. A platform can show you where to start but cannot rewrite your deployment code.
Frequently asked questions
What is a service principal in simple terms?
It is a cloud identity for an application, script, or automation, so that software can sign in and act in the cloud with its own credentials and its own permissions, separate from any person.
What is the difference between an app registration and a service principal?
An app registration is the definition of an application. A service principal is the instance of that application in a particular tenant, and it is the thing that holds permissions and signs in. When you audit access, you review service principals.
What is a managed identity?
A managed identity is a service principal that Azure creates and manages for a resource, such as a virtual machine or function. It has no secret for you to store or rotate, which makes it safer than a service principal that uses a client secret.
Do service principals use multi-factor authentication?
No. They sign in with a secret, a certificate or a federated token. Whoever holds the credential can authenticate as the service principal, which is why protecting and limiting those credentials is so important.
Why are service principals a security risk?
They often hold broad permissions, use long-lived credentials, escape the controls that protect human logins, and have no clear owner. A leaked secret grants the full access of the identity, and the activity looks like normal automation.
How do I make service principals safer?
Inventory them and assign owners, use managed identities and federated credentials instead of secrets, apply least privilege, rotate and expire the secrets you must keep, restrict who can add credentials, monitor sign-ins, and delete those you no longer need.
Is a service principal the same as an AWS IAM role or a GCP service account?
They serve the same purpose, which is giving software an identity. The details differ by cloud. AWS roles are assumed to obtain temporary credentials, and GCP service accounts can be attached to resources or used with keys. The security principles are the same across all three.
