The requirements necessitate the deployment of a robust backup solution for Azure File shares with protection against deletion and retention period modification. The first step is to Create a Recovery Services vault, which is the required component for Azure Files backup. Next, Enable vault immutability to turn on protection against the deletion of backups and modification of the backup retention policy. Finally, Lock immutability for the vault makes the vault configuration permanent and irreversible. Locking immutability is a key feature that prevents all users, including administrators, from deleting the vault or modifying the protection settings, directly addressing the requirements to prevent deletion and modification, and preventing privilege escalation attacks on the backup solution's immutability settings.

Microsoft Azure Documentation: Backup Azure File shares

Specific Section: Prerequisites/Preparation steps.

Verifiability: A Recovery Services vault is required to back up Azure File shares, making it the essential initial deployment step for the solution.

Microsoft Azure Documentation: Manage immutability for Azure Recovery Services vaults

Specific Section: About Immutability/Security features.

Verifiability: Enabling vault immutability (step 2) ensures backups cannot be prematurely deleted and retention settings cannot be reduced or modified, directly meeting two core requirements.

Microsoft Azure Documentation: Lock immutability for Recovery Services vaults

Specific Section: Locking the vault immutability.

Verifiability: Locking the vault immutability (step 3) makes the protection irreversible by any user (including those with administrative privileges), thus preventing both privilege escalation attacks on the backup settings and meeting the stringent deletion and modification prevention requirements simultaneously.

Microsoft Azure Documentation: Resource Locks in Azure

Specific Section: Purpose of Resource Locks.

Verifiability: Resource locks primarily prevent accidental deletion or modification of the resource or resource group. While relevant for RG1, Locked immutability is the specific and most effective control for meeting the strict data and policy protection requirements inside the vault, making the resource lock action less critical than the three selected actions in this sequence.