cis-azure-storage-17-13

name	cis-azure-storage-17.13
description	Ensure that 'Allow Blob Anonymous Access' is set to 'Disabled'
category	cis-azure-storage
version	1.0.0
author	cyberstrike-official
tags	["cis","azure","storage","storage-accounts","encryption"]
cis_id	17.13
cis_benchmark	CIS Microsoft Azure Storage Services Benchmark v1.0.0
tech_stack	["azure"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

17.13 Ensure that 'Allow Blob Anonymous Access' is set to 'Disabled' (Automated)

Description

The Azure Storage setting 'Allow Blob Anonymous Access' (aka "allowBlobPublicAccess") controls whether anonymous access is allowed for blob data in a storage account. When this property is set to True, it enables public read access to blob data, which can be convenient for sharing data but may carry security risks. When set to False, it disallows public access to blob data, providing a more secure storage environment.

Rationale

If "Allow Blob Anonymous Access" is enabled, blobs can be accessed by adding the blob name to the URL to see the contents. An attacker can enumerate a blob using methods, such as brute force, and access them.

Exfiltration of data by brute force enumeration of items from a storage account may occur if this setting is set to 'Enabled'.

Impact

Additional consideration may be required for exceptional circumstances where elements of a storage account require public accessibility. In these circumstances, it is highly recommended that all data stored in the public facing storage account be reviewed for sensitive or potentially compromising data, and that sensitive or compromising data is never stored in these storage accounts.

Audit Procedure

Audit from Azure Portal

1. Go to Storage Accounts.
2. For each storage account, under Settings, click Configuration.
3. Ensure Allow Blob Anonymous Access is set to Disabled.

Audit from Azure CLI

For every storage account in scope:

az storage account show --name "<yourStorageAccountName>" --query allowBlobPublicAccess

Ensure that every storage account in scope returns false for the "allowBlobPublicAccess" setting.

Audit from Azure Policy

Policy ID: 4fa4b6c0-31ca-4c0d-b10d-24b96f62a751 - Name: '[Preview]: Storage account public access should be disallowed'

Expected Result

Allow Blob Anonymous Access should be set to Disabled for all storage accounts. CLI output should return false for allowBlobPublicAccess.

Remediation

Remediate from Azure Portal

1. Go to Storage Accounts.
2. For each storage account, under Settings, click Configuration.