How to Fix PostgreSQL 15 Permission Denied for Schema PUBLIC

PostgreSQL 15 introduced a significant security enhancement by revoking the CREATE permission from all users except the database owner in the public (or default) schema. This change aims to improve database security by preventing unintended table creation in the public schema, which can lead to vulnerabilities and data breaches. However, this change can cause confusion for users who are accustomed to creating tables in the public schema without explicit permissions. This article will explore the reasons behind this change, the implications for users, and provide a comprehensive solution for creating tables in the public schema as a non-superuser user.

Why the Change in PostgreSQL 15?

Prior to PostgreSQL 15, any user with CREATE privileges on the public schema could create tables within it, regardless of whether they were the database owner. This permissive behavior opened a potential security gap. Imagine a scenario where a user with limited privileges accidentally or intentionally creates a table in the public schema that exposes sensitive data. This data could be vulnerable to unauthorized access by other users with privileges on the public schema.

PostgreSQL 15 addresses this security concern by restricting CREATE permissions within the public schema. Only the database owner now has the ability to create tables directly in the public schema. This change promotes a more secure environment by limiting the potential impact of malicious or accidental actions, thereby protecting sensitive data.

Common User Scenarios and Solutions

Let's examine a common scenario where a user, admin, attempts to create a table in the public schema within a database mydb. The user has been granted all privileges on the database mydb but still encounters the "cannot create table in schema public" error.

Understanding the Problem:

The root of the problem lies in the way permissions are handled in PostgreSQL. The GRANT ALL ON DATABASE mydb TO admin; statement only grants privileges on the database itself. It doesn't automatically grant permissions to the public schema within that database. Therefore, admin still lacks the necessary permission to create tables in the public schema of mydb.

Solution 1: Granting Explicit Permissions on the Public Schema

The simplest and most secure solution is to explicitly grant the admin user USAGE and CREATE permissions on the public schema within the mydb database. This ensures that admin can only create tables in the public schema of mydb and no other database.

      GRANT USAGE, CREATE ON SCHEMA public TO admin; -- within the 'mydb' database
    

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Solution 2: Making admin the Owner of the Database

If you want to give admin complete control over the mydb database, including the public schema, you can change the database owner to admin. This grants admin full privileges on the database and its schemas, including the ability to create tables in the public schema.

      ALTER DATABASE mydb OWNER TO admin;
    

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Important Considerations:

• Security: Granting CREATE permissions on the public schema should be done cautiously. Carefully assess the need for such access and ensure you're granting it to trusted users.

• Schema Isolation: Consider creating separate schemas for different applications or users to enhance security and avoid conflicts.

• Best Practices: In general, avoid relying heavily on the public schema. Instead, create dedicated schemas for specific applications or users to promote a structured and secure database environment.

Understanding PostgreSQL's Schema Security Model

PostgreSQL 15's security enhancement underscores the importance of a well-defined schema structure and granular permission control. By default, new users are not granted access to create tables in the public schema. This encourages developers to create dedicated schemas for their applications, promoting better organization, security, and scalability.

Moving Forward with Secure Schema Usage

Here are some recommended practices for working with schemas in PostgreSQL:

• Create dedicated schemas: For every new application or user, create a dedicated schema to prevent conflicts and enhance security.

• Grant specific permissions: Avoid granting broad permissions to users. Instead, grant only the permissions they require to perform their tasks.

• Use the OWNER role: For users requiring full control over a database or schema, grant them the OWNER role to manage objects within that scope.

• Regularly review and adjust permissions: As your database evolves, periodically review user permissions and adjust them accordingly to maintain security and prevent unintended access.

Conclusion

PostgreSQL 15's change in schema security is a positive step towards enhancing database security and promoting best practices. By understanding the reasons behind this change and implementing the recommended solutions, developers can work effectively with PostgreSQL while maintaining a secure and well-structured database environment. Remember to consider the security implications of granting permissions and carefully evaluate your database structure to ensure data integrity and confidentiality.