The Secret Life of Azure: The Function App With CEO Privileges
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Exploring the risks of the Owner role and the quiet danger of granting a service the power to change its own rules.
ARC 1 — Identity & Access
The rain drummed against the library windows as Margaret adjusted the lamp on the table. She looked at a small diagram Timothy had been sketching in his notebook.
"Timothy," she said softly, "I noticed you were looking at the permissions for our new Function App. It’s a helpful little service, isn't it?"
Timothy looked up, leaning back in his chair. "It is. It’s meant to handle a few background tasks. But Margaret, I noticed something in the configuration that felt a bit heavy. It’s listed as an Owner at the Subscription level."
Margaret pulled a chair closer. "You have a sharp eye for detail. Tell me, why does that particular setting give you pause?"
"Well," Timothy said, tapping his pen on the paper, "isn't the Owner role more about managing the entire environment? If this code only needs to process a few files, why does it have the power to change the access policies for the whole team?"
The Permission to Change Permissions
"That is exactly the point," Margaret replied with a nod. "The Owner role includes the Microsoft.Authorization/*/Write permission. This means that if anyone were to gain control of that Function App, they wouldn't just be able to run code. They could grant themselves—or anyone else—permanent access to the entire Subscription."
Timothy frowned. "So the risk isn't just about what the code does, it's about what an attacker could do with its identity."
"Precisely," Margaret said. "In the cloud, we call that Privilege Escalation. It is a quiet risk that often goes unnoticed until it is too late. In practice, workloads almost never need the Owner role."
The Temptation of Convenience
"I suppose I'm wondering why someone would set it up that way to begin with," Timothy mused. "It seems like a lot of extra power to manage."
"It usually starts with a simple error," Margaret explained gently. "When an engineer sees a 403 'Unauthorized' message, it is tempting to apply the Owner role just to verify that the code can run. They tell themselves they will find a narrower role later, but as the work moves forward, that broad permission often stays in place."
Choosing a Narrower Path
Margaret picked up a piece of chalk and wrote two words on the board: Contributor and Reader.
"If we want to be responsible with our security, we have better options," she said. "If the app needs to manage resources, we can use the Contributor role. It allows the app to work, but it removes the power to change access rules. And if it only needs to look at data?"
Timothy smiled. "Then it’s just a Reader. It can see the logs and the status without being able to change a single thing."
Putting It into Practice
Timothy looked back at his notes, feeling much more at ease. "So, we should define the Function App by exactly what it needs to do right now, at the smallest possible scope. And of course, this assumes we are using a Managed Identity, which keeps our credentials off the desk and in the platform where they belong."
"Exactly," Margaret said, her tone warm. "By using roles like Reader or Contributor at the Resource Group level, we keep the environment stable. We give the service the space it needs to work, without giving it the power to change the rules for everyone else."
Key Concepts
- Owner Role: Grants full access to manage all resources and the ability to assign roles to others via the
Microsoft.Authorization/*/Writepermission. - Contributor Role: Allows the management of resources but specifically excludes the permission to manage access or assign roles.
- Reader Role: A restricted role that allows viewing resources and their settings but prevents any modifications.
- Privilege Escalation: A security risk where a principal with high permissions is used to gain even greater control over an environment.
- Least Privilege: The practice of providing an identity with only the minimum permissions and narrowest scope required for its specific task.
Aaron Rose is a software engineer and technology writer at tech-reader.blog and the author of Think Like a Genius.
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