Storage security rules in Firebase - Commands & Configuration

Introduction

Storage security rules control who can read or write files in your Firebase storage. They protect your files from unauthorized access and keep your data safe.

When you want only logged-in users to upload profile pictures.

When you want to allow public read access but restrict who can upload files.

When you want to prevent users from deleting or modifying files they do not own.

When you want to limit file uploads to certain file types or sizes.

When you want to secure sensitive documents so only specific users can access them.

Config File - storage.rules

storage.rules

rules_version = '2';
service firebase.storage {
  match /b/{bucket}/o {
    match /user_uploads/{userId}/{allPaths=**} {
      allow read, write: if request.auth != null && request.auth.uid == userId;
    }
    match /public/{allPaths=**} {
      allow read;
      allow write: if false;
    }
  }
}

This file defines Firebase Storage security rules.

rules_version specifies the version of the rules syntax.

The service firebase.storage block applies rules to your storage buckets.

The first match block allows users to read and write only their own files inside user_uploads/{userId} folders if they are logged in and their user ID matches the folder name.

The second match block allows anyone to read files in the public folder but denies all writes.

Commands

This command uploads and activates your storage security rules to Firebase. It ensures your rules are enforced immediately.

Terminal

firebase deploy --only storage

Expected Output

=== Deploying to 'your-project-id'...



i  deploying storage

✔  storage: rules storage.rules



✔  Deploy complete!



Project Console: https://console.firebase.google.com/project/your-project-id/overview

→

--only - Deploy only the specified Firebase feature, here storage rules.

This command downloads the currently active storage rules to a file named current.rules for review or backup.

Terminal

firebase storage:rules:get > current.rules

Expected Output

Rules downloaded to current.rules

This command tests if a user with ID abc123 can read the file photo.jpg in their user_uploads folder. It helps verify your rules work as expected.

Terminal

firebase storage:rules:test --path /user_uploads/abc123/photo.jpg --operation read --auth abc123

Expected Output

Test result: ALLOWED

→

--path - Specifies the file path to test.

→

--operation - Specifies the operation to test, like read or write.

→

--auth - Simulates the user ID for the test.

Key Concept

If you remember nothing else from this pattern, remember: storage security rules protect your files by controlling who can read or write based on user identity and file location.

Common Mistakes

Allowing write access to everyone by using 'allow write: if true;'

This lets anyone upload or delete files, risking data loss or abuse.

Restrict write access to authenticated users or specific user IDs only.

Not matching the user ID in the path with the authenticated user ID.

Users could access or modify other users' files, breaking privacy.

Use 'request.auth.uid == userId' in the rule to ensure users access only their own files.

Forgetting to deploy the updated rules after editing the file.

Changes won't take effect until deployed, leaving old rules active.

Run 'firebase deploy --only storage' after any rule changes.

Summary

Write storage security rules in the storage.rules file to control file access.

Deploy rules using 'firebase deploy --only storage' to activate them.

Test rules with 'firebase storage:rules:test' to ensure correct permissions.

Practice

1. What is the main purpose of Firebase Storage security rules?

easy

A. To control who can read or write files in storage

B. To speed up file uploads

C. To increase storage space automatically

D. To backup files to another server

Solution

1. Step 1: Understand the role of security rules

   Security rules define who can access files and what actions they can perform.

2. Step 2: Identify the main function

   The main function is to control read and write permissions to protect data.

3. Final Answer:

   To control who can read or write files in storage -> Option A

4. Quick Check:

   Security rules = control access [OK]

Hint: Security rules control access permissions only [OK]

Common Mistakes:

• Thinking rules speed up uploads
• Believing rules increase storage size
• Confusing rules with backup features

2. Which of the following is the correct syntax to allow only authenticated users to read files in Firebase Storage rules?

easy

A. allow read: if request.auth != null;

B. allow read: if user.authenticated == true;

C. allow read: if auth.user != null;

D. allow read: if request.user.authenticated;

Solution

1. Step 1: Check Firebase Storage rules syntax

   The correct way to check authentication is using request.auth != null.

2. Step 2: Compare options

   Only allow read: if request.auth != null; uses the correct Firebase syntax for authentication check.

3. Final Answer:

   allow read: if request.auth != null; -> Option A

4. Quick Check:

   Authentication check = request.auth != null [OK]

Hint: Use request.auth to check user authentication [OK]

Common Mistakes:

• Using incorrect variable names like user.authenticated
• Missing the 'request.' prefix
• Using wrong boolean checks

3. Given the following Firebase Storage rule snippet, what happens when an unauthenticated user tries to read a file?

service firebase.storage {
  match /b/{bucket}/o {
    match /files/{fileId} {
      allow read: if request.auth != null;
      allow write: if false;
    }
  }
}

medium

A. The read request causes a syntax error

B. The read request is allowed because write is false

C. The read request is allowed because no write permission is needed

D. The read request is denied because the user is not authenticated

Solution

1. Step 1: Analyze the read rule condition

   The rule allows read only if request.auth != null, meaning user must be authenticated.

2. Step 2: Consider unauthenticated user

   An unauthenticated user has request.auth == null, so the condition fails and read is denied.

3. Final Answer:

   The read request is denied because the user is not authenticated -> Option D

4. Quick Check:

   Unauthenticated read = denied [OK]

Hint: Read allowed only if request.auth is not null [OK]

Common Mistakes:

• Ignoring the read condition and assuming access
• Confusing read and write permissions
• Thinking false write affects read

4. Identify the error in this Firebase Storage rule that aims to allow users to write only to their own folder:

service firebase.storage {
  match /b/{bucket}/o {
    match /users/{userId}/{allPaths=**} {
      allow write: if request.auth.uid == userId;
    }
  }
}

medium

A. The variable userId is not defined in the path

B. The wildcard {allPaths=**} is incorrectly used

C. The rule does not allow read access

D. The condition should use request.auth.userId instead of request.auth.uid

Solution

1. Step 1: Check path variables

   The path correctly defines {userId} and {allPaths=**} wildcards.

2. Step 2: Review condition and permissions

   The condition correctly compares request.auth.uid with userId for write permission.

3. Step 3: Identify missing read permission

   The rule only allows write, no read permission is granted, which may block legitimate reads.

4. Final Answer:

   The rule does not allow read access -> Option C

5. Quick Check:

   Missing read permission = problem [OK]

Hint: Check if both read and write permissions are set [OK]

Common Mistakes:

• Assuming write permission covers read
• Confusing request.auth.uid with userId variable
• Misusing wildcard syntax

5. You want to allow users to upload images only to their own folder and only if the file size is less than 2MB. Which Firebase Storage rule correctly enforces this?

service firebase.storage {
  match /b/{bucket}/o {
    match /users/{userId}/{fileName} {
      allow write: if request.auth.uid == userId && request.resource.size < 2 * 1024 * 1024;
      allow read: if request.auth.uid == userId;
    }
  }
}

hard

A. The file size check should use resource.size instead of request.resource.size

B. This rule correctly enforces user ownership and file size limit

C. The rule should allow write without checking user ID

D. The size limit should be checked on the existing file, not request.resource

Solution

1. Step 1: Verify user ownership condition

   The rule checks request.auth.uid == userId to ensure users write only to their folder.

2. Step 2: Verify file size condition

   The rule uses request.resource.size < 2 * 1024 * 1024 to limit uploads to less than 2MB.

3. Step 3: Confirm read permission

   Read is allowed only for the authenticated user matching userId.

4. Final Answer:

   This rule correctly enforces user ownership and file size limit -> Option B

5. Quick Check:

   User ID and size check = correct [OK]

Hint: Use request.resource.size for new file size check [OK]

Common Mistakes:

• Using resource.size instead of request.resource.size
• Not checking user ID for write
• Checking size on existing file instead of upload