From /metrics to Money: How a Leaky Endpoint Bagged a ,000 Bounty + Video

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Introduction:

In the high-stakes world of bug bounty hunting, the most severe vulnerabilities often don’t require complex SQL injection or memory corruption. Sometimes, they are simply left out in the open, waiting for someone with the right reconnaissance skills to look. This analysis delves into a recent $1,000 bounty win where a team discovered an unauthenticated /metrics endpoint leaking live, plaintext secrets. We will explore the technical breakdown of this information disclosure, the potential for exploitation, and the critical mitigation strategies every organization must adopt.

Learning Objectives:

  • Understand the risks associated with exposed monitoring and metrics endpoints.
  • Learn how to discover and audit /metrics endpoints during reconnaissance.
  • Identify common secrets (API keys, tokens) leaked in plaintext.
  • Implement access control and security measures for internal infrastructure endpoints.
  • Apply practical Linux and CLI commands for secret discovery and verification.

You Should Know:

  1. The Anatomy of the Leak: Understanding the /metrics Endpoint
    The /metrics endpoint is a standard feature in modern application development, commonly used by tools like Prometheus for monitoring and performance logging. By design, it is meant to export data about the application’s runtime, but misconfigurations can turn it into a treasure trove for attackers. In this case, the endpoint was left completely unauthenticated, exposing sensitive data including Solana RPC API Keys and Segment Analytics Keys.

Step‑by‑step guide explaining what this does and how to use it.
To understand what was exposed, one must first be able to identify and inspect such endpoints. Here’s how a security researcher might approach this:

  1. Reconnaissance with FFUF or Dirb: Use directory fuzzing tools to discover hidden endpoints. 
    Using ffuf to fuzz for common monitoring paths
ffuf -u https://target.com/FUZZ -w /usr/share/wordlists/seclists/Discovery/Web-Content/common.txt -mc 200

Look for results like `/metrics`, `/health`, `/status`, `/debug/vars`.

  1. Inspecting the Endpoint: Once found, use `curl` to fetch the data and look for patterns. 
    curl -s https://target.com/metrics | head -n 50

    This command will show the raw output. In the case of the bounty, the output would have contained lines resembling:

    solana_rpc_key="secret_abc123..."
segment_write_key="DEF456..."

  2. Verifying the Leak: To confirm if a key is live and valid, you might attempt a benign API call (without causing harm) or simply check its format against public documentation.

    Example: Checking if a Solana RPC endpoint responds (Do not use stolen keys)
curl -X POST https://api.mainnet-beta.solana.com -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","id":1, "method":"getHealth"}'

2. Exploitation Scenario: From Leak to Blockchain Heist

The discovery of a Solana RPC API key is particularly dangerous. An RPC (Remote Procedure Call) key allows an application to interact directly with the Solana blockchain. If the exposed key had write permissions, an attacker could have drained wallets, manipulated smart contracts, or performed unauthorized transactions.

Step‑by‑step guide explaining the potential impact.

While we do not advocate for illegal activity, understanding the exploitation chain is vital for defense.

  1. Identifying the RPC Endpoint: The leaked key is likely tied to a specific Solana RPC provider (e.g., Helius, QuickNode, or a private node). The researcher would identify the base URL associated with the key.

  2. Testing Capabilities: An attacker would test what methods the key allows.

    Testing if the key allows transaction simulation (a harmless test)
curl -X POST <RPC_ENDPOINT_URL> \
-H "Content-Type: application/json" \
-d '{
"jsonrpc": "2.0",
"id": 1,
"method": "simulateTransaction",
"params": [...]
}'

  3. Potential Financial Impact: If the key allowed for sendTransaction, the attacker could craft a transaction moving funds from a vulnerable wallet they identified through other recon, or simply use the compute units provided by the key to run their own scripts for free, incurring massive costs for the key owner.

3. Hunting for Secrets with Grep and Regex

When auditing a large /metrics dump or any web response, manually sifting through lines of text is inefficient. Security professionals use regex patterns to hunt for specific data formats.

Step‑by‑step guide explaining this automated discovery.

You can use `grep` with extended regular expressions to automate the hunt for secrets in a downloaded file.

  1. Save the Output: First, save the endpoint data locally. 
    curl -s https://target.com/metrics > metrics_dump.txt

  2. Search for API Key Patterns: Use regex to find common key patterns.

    Search for Solana/blockchain keys (example pattern)
grep -E '([A-Za-z0-9]{40,})' metrics_dump.txt

Search for AWS keys (a common find)
grep -E 'AKIA[0-9A-Z]{16}' metrics_dump.txt

Search for Slack tokens
grep -E 'xox[bash]-[0-9]{12}-[0-9]{12}-[a-zA-Z0-9]{24}' metrics_dump.txt

  3. Contextualize the Find: It is important to look at the lines surrounding the match to understand what the key is for.

    grep -B 2 -A 2 -E 'secret|key|token' metrics_dump.txt

4. Mitigation: Locking Down the Prometheus Scrape Target

The fix implemented by the target organization was to restrict access to the endpoint. In a cloud-native or Kubernetes environment, this involves network policies and web server configurations.

Step‑by‑step guide explaining the secure configuration.

For an organization running a metrics endpoint, here is how to secure it properly:

  1. Implement Authentication: If using Prometheus, configure it to use basic authentication or bearer tokens.

Prometheus.yml example:

scrape_configs:
- job_name: 'secure-app'
scheme: https
basic_auth:
username: 'prometheus_user'
password: 'strong_password_hash'
static_configs:
- targets: ['app-server:9090']
  1. Network Segmentation: Use firewalls or security groups to allow access only from the Prometheus server’s IP address.

Nginx configuration to block external access:

location /metrics {
allow 192.168.1.100;  Allow internal monitoring IP
deny all;
proxy_pass http://localhost:8080/metrics;
}
  1. mTLS in Service Meshes: In advanced setups like Istio or Linkerd, enforce mutual TLS (mTLS) so that only services with a valid certificate can access the endpoint.

5. Secure Development: Secrets Management

The root cause of this vulnerability is that secrets were stored in a location accessible by the application’s metrics module. This violates the principle of separating code from configuration.

Step‑by‑step guide explaining secure secret handling.

Instead of hardcoding secrets into environment variables that get dumped, use a dedicated secrets manager.

  1. Hashicorp Vault Integration: Applications should authenticate to Vault and request secrets on the fly.
  2. Kubernetes Secrets: If using Kubernetes, mount secrets as volumes or environment variables, ensuring they are not logged. 
    apiVersion: v1
kind: Pod
metadata:
name: my-app
spec:
containers:</li>
</ol>

- name: my-app
image: my-app:latest
env:
- name: SEGMENT_KEY
valueFrom:
secretKeyRef:
name: app-secrets
key: segment-key

    3. Audit Environment Variables: Regularly scan running containers to ensure no secrets are exposed via `/proc/self/environ` or debug endpoints.

    6. Windows Equivalent: Auditing IIS for Exposed Endpoints

    While the original hack targeted a Linux-based application, Windows servers are equally guilty of exposing debug endpoints, particularly via IIS or ASP.NET applications.

    Step‑by‑step guide explaining the Windows approach.

    Security researchers auditing a Windows target should look for similar exposure.

    1. Check for Debug Paths: Use tools like `Invoke-WebRequest` in PowerShell to probe for endpoints. 
      Invoke-WebRequest -Uri "https://target.com/metrics" -Method Get
Invoke-WebRequest -Uri "https://target.com/healthchecks" -Method Get

    2. IIS URL Rewrite for Blocking: On the defensive side, an admin can use IIS URL Rewrite to block access to these paths.

    Web.config snippet:

    <system.webServer>
<rewrite>
<rules>
<rule name="Block Metrics" stopProcessing="true">
<match url="^metrics$" />
<action type="CustomResponse" statusCode="403" statusReason="Forbidden" />
</rule>
</rules>
</rewrite>
</system.webServer>
    1. Remove Debug Compilation Flags: Ensure that ASP.NET applications are not compiled with debug flags set to true, as this can expose detailed error messages and variable dumps.

    What Undercode Say:

    • Key Takeaway 1: Reconnaissance is King. This bounty was won not by complex exploitation, but by thorough reconnaissance. Always map the entire attack surface, including “internal-only” paths.
    • Key Takeaway 2: Defense in Depth for Monitoring. Metrics endpoints are critical for operations but must be treated as sensitive as production databases. They require strict authentication and network controls.

    This incident is a classic example of how automation and observability tools can become an organization’s weakest link if not properly configured. The team’s quick discovery and responsible disclosure highlight the essential role of ethical hackers in modern cybersecurity. For defenders, the lesson is clear: conduct regular audits of your publicly accessible endpoints. Assume that if an endpoint exists and is unauthenticated, it will be found and scraped by bad actors. The fix is often simple—a firewall rule, a reverse proxy configuration, or a secret rotation policy—but the impact of ignoring it can be catastrophic, leading to financial loss and complete system compromise.

    Prediction:

    As more companies adopt blockchain technology and microservices architectures, the number of exposed /metrics and /debug endpoints will initially rise. Attackers will increasingly automate the scraping of these endpoints specifically to find Solana, Ethereum, and other high-value RPC keys. This will lead to a surge in “supply chain” style attacks where the initial breach vector is not the main application, but a supporting monitoring tool. Consequently, we predict that the next evolution of Web Application Firewalls (WAFs) will include specific signatures to detect and block directory fuzzing for these sensitive paths, and secrets management will become a mandatory compliance requirement for handling cryptocurrency infrastructure.

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