How to remediate – Google Cloud Build Configuration Detected

1. Introduction

Google Cloud Build Configuration Detected refers to the presence of a `cloudbuild.yaml` file within your source code repositories. This configuration file defines build workflows for Google Cloud’s continuous integration and deployment platform. Exposing this file can allow attackers to gain insight into your application’s build process, potentially revealing sensitive information or allowing them to inject malicious commands. A successful exploit could compromise the confidentiality of credentials and other secrets used in your builds.

2. Technical Explanation

The vulnerability arises from misconfigured permissions on `cloudbuild.yaml` files, making them accessible via a web server. An attacker can then read this file to understand build steps and potentially extract sensitive data like API keys or passwords used during the build process. The primary exploit mechanism involves directly accessing the exposed configuration file through a web browser or using tools like `curl` or `wget`.

• Root cause: Improperly configured permissions on the `cloudbuild.yaml` file, allowing public access.
• Exploit mechanism: An attacker accesses the publicly accessible `cloudbuild.yaml` file via HTTP/HTTPS to view build configurations and potentially extract sensitive information. For example, an attacker could navigate to https://example.com/repository/.github/workflows/cloudbuild.yaml if the file is located in a public repository directory.
• Scope: Applications using Google Cloud Build with publicly exposed `cloudbuild.yaml` files are affected.

3. Detection and Assessment

To confirm vulnerability, check for accessible `cloudbuild.yaml` files within your web application’s file structure. A thorough method involves scanning the entire codebase and web server directories for these configuration files.

• Quick checks: Use a web browser to attempt access to common locations like /cloudbuild.yaml, /.github/workflows/cloudbuild.yaml or other repository paths.
• Scanning: Nessus plugin ID 16389 can identify exposed `cloudbuild.yaml` files. Burp Suite’s spider functionality can also be used to crawl for these files. These are examples only and may require configuration.
• Logs and evidence: Web server access logs might show requests for `cloudbuild.yaml` or related files, indicating potential reconnaissance activity.

curl https://example.com/repository/.github/workflows/cloudbuild.yaml

4. Solution / Remediation Steps

To fix the issue, ensure `cloudbuild.yaml` files are not deployed with your application or are protected from web access. Revoke and reset any credentials found in exposed files.

4.1 Preparation

• Ensure you have a rollback plan by keeping a copy of the original configuration file.
• A change window may be required depending on service impact. Approval from security or IT operations may be needed.

4.2 Implementation

1. Step 1: Review your deployment process to identify where `cloudbuild.yaml` files are being copied.
2. Step 2: Exclude the `cloudbuild.yaml` file from web server directories in your deployment configuration.
3. Step 3: Set appropriate file permissions on any remaining `cloudbuild.yaml` files, restricting access to authorized users only (e.g., using chmod 600).
4. Step 4: If sensitive information was found in an exposed file, revoke and reset the affected credentials.

4.3 Config or Code Example

Before

# .htaccess file allowing access to all files
<FilesMatch ".(yaml|yml)$">
  Allow from all
</FilesMatch>

After

# .htaccess file denying access to yaml/yml files in web directories
<FilesMatch ".(yaml|yml)$">
  Order deny,allow
  Deny from all
</FilesMatch>

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this issue. Least privilege reduces the impact of a compromise if an attacker gains access. Secure configuration management ensures files are protected with appropriate permissions.

• Practice 1: Implement least privilege principles, granting only necessary access to resources and data.
• Practice 2: Enforce secure configuration management practices, including proper file permissions and regular security audits.

4.5 Automation (Optional)

If using Infrastructure as Code (IaC), update your templates to exclude `cloudbuild.yaml` files from web server directories automatically.

# Example Terraform snippet
resource "aws_s3_bucket" "example" {
  ...
  tags = {
    ExcludeFromWebAccess = ["cloudbuild.yaml"]
  }
}

5. Verification / Validation

Confirm the fix by verifying that `cloudbuild.yaml` files are no longer accessible via a web browser or direct HTTP/HTTPS request. Perform a smoke test to ensure application functionality remains intact.

• Post-fix check: Attempt to access the previously exposed `cloudbuild.yaml` file using curl https://example.com/repository/.github/workflows/cloudbuild.yaml. Expect an HTTP 403 Forbidden error.
• Re-test: Repeat the quick checks from Section 3 and confirm that no `cloudbuild.yaml` files are accessible.
• Smoke test: Verify core application functionality, such as user login or data retrieval, to ensure the fix did not introduce regressions.
• Monitoring: Monitor web server access logs for any further requests for `cloudbuild.yaml` files.

curl https://example.com/repository/.github/workflows/cloudbuild.yaml - should return 403 Forbidden

6. Preventive Measures and Monitoring

Update security baselines to include restrictions on exposing sensitive configuration files. Implement CI/CD pipeline checks to prevent deployment of these files to web server directories. A regular patch review cycle can help identify and address misconfigurations promptly.

• Baselines: Update your security baseline or policy to explicitly prohibit the deployment of `cloudbuild.yaml` files to publicly accessible web servers.
• Asset and patch process: Implement a regular review cycle for application configurations, including file permissions and access controls.

7. Risks, Side Effects, and Roll Back

• Risk or side effect 1: Incorrect file permissions may prevent legitimate users from accessing necessary resources.
• Risk or side effect 2: Changes to deployment processes could introduce unintended consequences.

8. References and Resources

• Vendor advisory or bulletin: https://cloud.google.com/build
• NVD or CVE entry: No specific CVE is associated with this configuration issue, but it relates to CWE-16 and CWE-