11.4 Ensure stored access policies (SAP) are used when generating shared access signature (SAS) tokens (Manual)
Description
Use stored access policies (SAP) when generating shared access signature (SAS) tokens in Azure to centrally manage permissions, expiration, and revocation settings for resource access. Stored access policies can be applied to blob containers, file shares, queues, and tables.
Rationale
Stored access policies provide centralized control over SAS token access, allowing administrators to update permissions or revoke access. This approach strengthens security by reducing the risk of unauthorized access to storage resources.
Impact
There is no cost for creating stored access policies, however there is some administrative overhead involved in managing these policies.
Audit Procedure
It is not currently possible to retrieve a list of all generated SAS tokens to check if they were associated with a SAP during creation.
An SAS token that has been created with a SAP will contain an si parameter that references the stored access policy identifier associated with the SAS, e.g. si=<stored-access-policy-identifier>.
The si parameter will be absent from an SAS token created without a SAP.
Expected Result
All SAS tokens contain an si parameter referencing a stored access policy identifier.
Remediation
Remediate from Azure Portal
To create a SAP for a blob container:
- Go to
Storage accounts.
- Click on a storage account.
- Under
Data storage, click Containers.
- Click the name of a container.
- Under
Settings, click Access policy.
- Under
Stored access policies, click + Add policy.
- Enter an
Identifier.
- From the
Permissions drop-down, select appropriate permissions for the policy.
- Set an appropriate
Start time for the policy.
- Set an appropriate
Expiry time for the policy.
- Click
OK.
- Click
Save.
- Repeat steps 1-12 as needed to create SAP.
When generating SAS, select a SAP from the Stored access policy drop-down.
If SAS have been created without a SAP, the SAS can be revoked by regenerating the storage account access keys:
Note: Regenerating access keys can affect any applications or Azure services that are dependent on the storage account key.
- Go to
Storage accounts.
- Click on a storage account.
- Under
Security + networking, click Access keys.
- Next to each key, click
Rotate key.
- Click
Yes to confirm.
- Repeat steps 1-5 as needed to revoke SAS.
Default Value
By default, stored access policies are not associated with SAS. To use a stored access policy, it must be explicitly created and linked to the SAS at the time of creation.
References
- https://learn.microsoft.com/en-us/azure/storage/common/storage-sas-overview#best-practices-when-using-sas
- https://learn.microsoft.com/en-us/rest/api/storageservices/define-stored-access-policy
Additional Information
This recommendation is based on the recommendation Ensure stored access policies (SAP) are used when generating shared access signature (SAS) tokens, from the Common Reference Recommendations > Secrets and Keys > Shared Access Signatures section.
Profile
Level 1 | Manual
