cyberstrikeus 16.2 Ensure that shared access signature (SAS) tokens expire within an hour (Manual)
Description
Shared access signature (SAS) tokens provide restricted access to Azure Storage resources (such as blobs, files, queues, or tables) for a defined time period with specific permissions. It enables users to interact with the resources without exposing account keys, offering precise control over the permitted actions (e.g., read, write) and the duration of access. To minimize security risks, SAS tokens should be configured with the shortest possible lifespan, ideally lasting no longer than an hour.
Rationale
A short lifespan for SAS tokens is recommended to minimize the risk of unauthorized access. SAS tokens grant time-limited access to resources, and a longer duration increases the opportunity for misuse if the token is compromised. By setting a shorter lifespan, the potential for security breaches is reduced.
Impact
SAS can pose security risks if they are not managed carefully.
Audit Procedure
Currently, SAS token expiration times cannot be audited. Until Microsoft makes the token expiration time a setting rather than a token creation parameter, this recommendation will require manual verification.
Expected Result
All shared access signature (SAS) tokens should be configured with an expiration time of one hour or less from the time of creation.
Remediation
Remediate from Azure Portal
If SAS have been created without a short lifespan and were created with a stored access policy (SAP), the SAS can be revoked by deleting the SAP or updating the SAP expiration time to a time in the past:
- Go to
Storage accounts. - Click on a storage account.
- Under
Data storage, clickQueues. - Click the three dots next to a listed item.
- Click
Access policy. - Click the three dots next to an access policy.
- Click
Delete. - Click
Save. - Repeat steps 1-8 as needed to revoke SAS created with SAP.
If SAS have been created without a short lifespan and were not created with 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, clickAccess keys. - Next to each key, click
Rotate key. - Click
Yesto confirm. - Repeat steps 1-5 as needed to revoke SAS.
Default Value
By default, expiration for shared access signature is set to 8 hours.
References
- https://docs.microsoft.com/en-us/azure/storage/common/storage-sas-overview
- https://docs.microsoft.com/en-us/rest/api/storageservices/delegating-access-with-a-shared-access-signature
Additional Information
This recommendation is based on the recommendation Ensure that shared access signature (SAS) tokens expire within an hour, from the Common Reference Recommendations > Secrets and Keys > Shared Access Signatures section.
CIS Controls
| Controls Version | Control | IG 1 | IG 2 | IG 3 |
|---|---|---|---|---|
| v8 | 6.2 Establish an Access Revoking Process - Establish and follow a process, preferably automated, for revoking access to enterprise assets, through disabling accounts immediately upon termination, rights revocation, or role change of a user. Disabling accounts, instead of deleting accounts, may be necessary to preserve audit trails. | X | X | X |
| v7 | 16.7 Establish Process for Revoking Access - Establish and follow an automated process for revoking system access by disabling accounts immediately upon termination or change of responsibilities of an employee or contractor. Disabling these accounts, instead of deleting accounts, allows preservation of audit trails. | X | X |
Profile
Level 1 | Manual