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Why Am I Getting a “403 Forbidden” Error in Blob Storage?

November 25, 2024 · 7 minutes read

Reviewed by: Dr. Maya

Table of Contents

The 403 Forbidden error in Azure Blob Storage typically occurs when there’s an issue with access permissions, authentication, or the URL being used to access the blob. Below are common causes and solutions to troubleshoot and resolve this error.


1. Authentication Issues

Cause: You might not be authenticated correctly, or the authentication token (shared access signature or Azure AD token) has expired or is invalid.

Solutions:

  1. Verify Authentication Method:
    • If using Azure AD, ensure your token is valid and has not expired.
      az account get-access-token
    • If using a Shared Access Signature (SAS), confirm that the token is active and matches the required permissions.
  2. Renew the SAS Token:
    • Generate a new SAS token via the Azure Portal or CLI.
      az storage container generate-sas --account-name <storage_account_name> --name <container_name> --permissions <permissions> --expiry <expiry_time>
  3. Reauthenticate:
    • If using Azure Storage Explorer, sign out and sign back in.

2. Insufficient Permissions

Cause: Your user account, service principal, or managed identity doesn’t have the necessary permissions to access the blob or container.

Solutions:

  1. Verify Role Assignments:
    • Go to Azure Portal > Storage Account > Access Control (IAM) and ensure your identity is assigned a role with blob access, such as:
      • Storage Blob Data Contributor
      • Storage Blob Data Owner
  2. Check Container Permissions:
    • Ensure the container’s access level allows the intended operation:
      • Private (default)
      • Blob (read-only public access to blobs)
      • Container (read-only public access to container and blobs).

3. Firewall or Network Restrictions

Cause: Your IP or virtual network might be blocked by the storage account’s network security settings.

Solutions:

  1. Allow Public Access:
    • If you’re accessing blobs anonymously, ensure public access is enabled in Configuration > Allow Blob Public Access.
  2. Add Your IP to the Allow List:
    • Go to Networking > Firewalls and Virtual Networks and add your IP address or range to the Allow list.
  3. Validate VNet Rules:
    • Ensure your virtual network and subnet are added to the storage account’s network rules.

4. Invalid URL or Incorrect Access Point

Cause: The URL you’re using to access the blob or container might be malformed or expired.

Solutions:

  1. Validate URL Format:
    • A proper blob URL looks like:
      https://<storage_account_name>.blob.core.windows.net/<container_name>/<blob_name>
  2. Verify SAS Parameters:
    • Check that the SAS token parameters, such as sp, st, and se, are correct.
  3. Check DNS Resolution:
    • Ensure the DNS resolves the correct storage endpoint.

5. Overwritten SAS or Access Policies

Cause: If you’re using SAS tokens tied to a stored access policy, changes to the policy (e.g., revoked permissions) can invalidate the token.

Solutions:

  1. Check Access Policies:
    • Go to the container in Azure Portal and verify stored access policies under Container > Access Policies.
  2. Regenerate SAS Tokens:
    • Create new tokens tied to the updated policy.

6. Account Keys Rotated

Cause: If the storage account keys were rotated, any SAS tokens generated with the old keys will no longer work.

Solution:

  • Generate new SAS tokens using the updated keys.

7. Storage Account Configuration Issues

Cause: Configuration settings such as secure transfer or encryption requirements might block access.

Solutions:

  1. Ensure Secure Transfer:
    • If secure transfer is enabled, ensure you’re using HTTPS instead of HTTP.
  2. Check Encryption Settings:
    • Confirm encryption requirements align with your connection.

8. Legacy Authentication Protocols

Cause: You might be attempting to access the blob using a deprecated authentication protocol or legacy application.

Solutions:

  1. Update Authentication:
    • Use Azure AD or SAS tokens instead of account keys where possible.
  2. Enable Legacy Protocols Temporarily:
    • If required, enable legacy protocols in Configuration > Allow Blob Public Access (not recommended for long-term use).

Troubleshooting Commands and Tools

  1. Check Access Using Azure CLI:
    az storage blob list --container-name <container_name> --account-name <storage_account_name>
    • Use this to verify if you can list blobs in the container.
  2. Use Azure Storage Explorer:
    • Test access and permissions using this GUI tool.
  3. Monitor Logs:
    • Check Azure Storage logs under Monitoring > Diagnostics Settings for more details about failed access attempts.

Summary

A 403 Forbidden error in Azure Blob Storage usually indicates issues with authentication, permissions, or network configurations. By systematically verifying your SAS tokens, role assignments, network rules, and storage account settings, you can quickly resolve the issue. Regularly review your policies and configurations to prevent recurrence.

For more detailed troubleshooting guides, follow Cerebrix on social media at @cerebrixorg

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Franck Kengne

Tech Visionary and Industry Storyteller

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