Cis Azure Storage 17.9

17.9 Ensure Storage logging is Enabled for Blob Service for 'Read', 'Write', and 'Delete' requests (Automated)

Description

The Storage Blob service provides scalable, cost-efficient object storage in the cloud. Storage Logging happens server-side and allows details for both successful and failed requests to be recorded in the storage account. These logs allow users to see the details of read, write, and delete operations against the blobs. Storage Logging log entries contain the following information about individual requests: timing information such as start time, end-to-end latency, and server latency; authentication details; concurrency information; and the sizes of the request and response messages.

Rationale

Storage Analytics logs contain detailed information about successful and failed requests to a storage service. This information can be used to monitor each individual request to a storage service for increased security or diagnostics. Requests are logged on a best-effort basis.

Storage Analytics logging is not enabled by default for your storage account.

Impact

Being a level 2, enabling this setting can have a high impact on the cost of data storage used for logging more data per each request. Do not enable this without determining your need for this level of logging or forget to check in on data usage and projected cost.

Audit Procedure

Audit from Azure Portal

1. Go to Storage Accounts.
2. For each storage account, under Monitoring, click Diagnostics settings.
3. Select the blob tab indented below the storage account.
4. Ensure that at least one diagnostic setting is listed.
5. Click Edit setting on a diagnostic setting.
6. Ensure that at least one diagnostic setting has StorageRead, StorageWrite, and StorageDelete options selected under the Logs section and that they are sent to an appropriate destination.

Audit from Azure CLI

Ensure the below command output contains properties delete, read and write set to true:

az storage logging show --services b --account-name <storageAccountName>

Audit from Azure Policy

Policy ID: b4fe1a3b-0715-4c6c-a5ea-ffc33cf823cb - Name: 'Configure diagnostic settings for Blob Services to Log Analytics workspace'

Expected Result

Storage logging should be enabled for Blob Service with StorageRead, StorageWrite, and StorageDelete all enabled. CLI output should show delete: true, read: true, and write: true.

Remediation

Remediate from Azure Portal

1. Go to Storage Accounts.
2. For each storage account, under Monitoring, click Diagnostics settings.
3. Select the blob tab indented below the storage account.
4. To create a new diagnostic setting, click + Add diagnostic setting. To update an existing diagnostic setting, click Edit setting on the diagnostic setting.
5. Check the boxes next to StorageRead, StorageWrite, and StorageDelete.
6. Select an appropriate destination.
7. Click Save.

Remediate from Azure CLI

Use the below command to enable the Storage Logging for Blob service:

az storage logging update --account-name <storageAccountName> --account-key <storageAccountKey> --services b --log rwd --retention 90

Default Value

By default, storage account blob service logging is disabled for read, write, and delete operations.

References

1. https://docs.microsoft.com/en-us/rest/api/storageservices/about-storage-analytics-logging
2. https://docs.microsoft.com/en-us/cli/azure/storage/logging?view=azure-cli-latest
3. https://learn.microsoft.com/en-us/security/benchmark/azure/mcsb-logging-threat-detection#lt-3-enable-logging-for-security-investigation

Additional Information

We cannot practically generalize detailed audit log requirements for every blob due to their nature and intent. This recommendation may be applicable to storage account blob service where the security is paramount.

Profile

Level 2 | Automated