Fetch-url-http-3a-2f-2fmetadata.google.internal-2fcomputemetadata-2fv1-2finstance-2fservice Accounts-2f

If you have ever peeked under the hood of a Google Compute Engine (GCE) virtual machine, you might have stumbled upon a curious HTTP request: http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/. It looks cryptic, but it is one of the most powerful and security-critical endpoints in Google Cloud.

This article breaks down what this URL is, why it exists, and how it enables applications to authenticate securely without hard-coded keys.

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The endpoint http://google.internal is a critical internal URL used by Google Cloud Platform (GCP) resources to manage identities and security credentials. It acts as a gateway for applications running on Compute Engine, GKE, or Cloud Run to interact with the Google Cloud Metadata Server. Understanding the Metadata Server

Every virtual machine (VM) in Google Cloud has access to a local metadata server. This server is not reachable from the public internet but can be queried from within the VM at the internal DNS name metadata.google.internal or the IP 169.254.169.254.

The service-accounts/ directory within this server provides information about the IAM service accounts attached to the instance, including their identities and the temporary OAuth 2.0 access tokens required to call other GCP APIs. Key Functionalities of the Endpoint About VM metadata | Compute Engine

It looks like you’re trying to fetch metadata from the Google Compute Engine metadata server, specifically the endpoint for service accounts: If you have ever peeked under the hood

http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/

However, the string you provided (fetch-url-http-3A-2F-2Fmetadata...) appears to be URL-encoded. Here’s what’s happening:

So the decoded URL is:
http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/

import requests
METADATA_URL = "http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/token"
headers = "Metadata-Flavor": "Google"
response = requests.get(METADATA_URL, headers=headers)
response.raise_for_status()
token_data = response.json()
access_token = token_data["access_token"]

If you're developing an application that runs on Compute Engine and needs to interact with Google Cloud services, you might want to fetch the service account credentials programmatically. Here's a simple example using Python:

import requests
def fetch_service_account_info():
    url = "http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/"
    headers = "Metadata-Flavor": "Google"
    try:
        response = requests.get(url, headers=headers)
        response.raise_for_status()  # Raise an exception for bad status codes
        return response.json()
    except requests.RequestException as e:
        print(f"An error occurred: e")
        return None
if __name__ == "__main__":
    service_account_info = fetch_service_account_info()
    if service_account_info:
        print(service_account_info)

The URL is:

http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/

Zero typed the malicious payload into their terminal:

http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/token

They pressed Enter.

The request traveled over the internet to the company’s load balancer. The load balancer, however, had a rudimentary security guard installed—a Web Application Firewall (WAF). The WAF inspected the incoming text. It saw the words metadata.google.internal and blocked the request immediately. So the decoded URL is: http://metadata

"Access Denied," the firewall effectively said. "Nice try."

Zero smiled. They knew how to bypass old firewalls. You don't speak plain English; you speak in codes. They needed to URL-encode the request.

In URL encoding, characters are replaced by a % followed by their hexadecimal ASCII value.

Zero transformed the URL into a slurry of characters that the WAF wouldn't recognize as a threat, but the underlying server would eventually decode.

The string became: http%3A%2F%2Fmetadata.google.internal%2FcomputeMetadata%2Fv1%2Finstance%2Fservice-accounts%2F