Secret leaks often occur when a sensitive piece of authentication data is stored with the source code of an application. Considering the source code is intended to be deployed across multiple assets, including source code repositories or application hosting servers, the secrets might get exposed to an unintended audience.

Why is this an issue?

In most cases, trust boundaries are violated when a secret is exposed in a source code repository or an uncontrolled deployment environment. Unintended people who don’t need to know the secret might get access to it. They might then be able to use it to gain unwanted access to associated services or resources.

The trust issue can be more or less severe depending on the people’s role and entitlement.

What is the potential impact?

The consequences vary greatly depending on the situation and the secret-exposed audience. Still, two main scenarios should be considered.

Financial loss

Financial losses can occur when a secret is used to access a paid third-party-provided service and is disclosed as part of the source code of client applications. Having the secret, each user of the application will be able to use it without limit to use the third party service to their own need, including in a way that was not expected.

This additional use of the secret will lead to added costs with the service provider.

Moreover, when rate or volume limiting is set up on the provider side, this additional use can prevent the regular operation of the affected application. This might result in a partial denial of service for all the application’s users.

Application’s security downgrade

A downgrade can happen when the disclosed secret is used to protect security-sensitive assets or features of the application. Depending on the affected asset or feature, the practical impact can range from a sensitive information leak to a complete takeover of the application, its hosting server or another linked component.

For example, an application that would disclose a secret used to sign user authentication tokens would be at risk of user identity impersonation. An attacker accessing the leaked secret could sign session tokens for arbitrary users and take over their privileges and entitlements.

How to fix it in ARM Templates

Code examples

Noncompliant code example

{
  "$schema": "https://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
  },
  "resources": [
    {
      "type": "Microsoft.Sql/servers",
      "apiVersion": "2023-05-01-preview",
      "name": "example-database",
      "properties": {
        "administratorLogin": "admin",
        "administratorLoginPassword": "password"
      }
    }
  ]
}

Compliant solution

{
  "$schema": "https://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "adminUsername": {
      "type": "securestring"
    },
    "adminPassword": {
      "type": "securestring"
    }
  },
  "resources": [
    {
      "type": "Microsoft.Sql/servers",
      "apiVersion": "2023-05-01-preview",
      "name": "example-database",
      "properties": {
        "administratorLogin": "[parameters('adminUsername')]",
        "administratorLoginPassword": "[parameters('adminPassword')]"
      }
    }
  ]
}

How to fix it in Bicep

Code examples

Noncompliant code example

resource sqlServer 'Microsoft.Sql/servers@2023-05-01-preview' = {
  name: 'example-database'
  properties: {
    administratorLogin: 'admin'
    administratorLoginPassword: 'password'
  }
}

Compliant solution

@secure()
param adminLogin string
@secure()
param adminPassword string

resource sqlServer 'Microsoft.Sql/servers@2023-05-01-preview' = {
  name: 'example-database'
  properties: {
    administratorLogin: adminLogin
    administratorLoginPassword: adminPassword
  }
}

Resources

Documentation

Standards