Header Hunt: Finding a Leaked Debug Header in Production

https://dashboard.webverselabs-pro.com/learning-paths/junior-web-hacker

Overview

Arc Logistics, a regional freight carrier, launched a public shipment tracking portal. According to the briefing, a debugging branch was merged the night before launch and nobody reviewed what was left behind. The objective is to identify the developer artifact that reached production and retrieve the exposed flag.

Reconnaissance

The landing page is a standard tracking interface with a single input field ("Tracking #") and a "Track Now" button. Nothing visible on the front end

discloses sensitive information. Since the page itself offered nothing, I proxied the traffic through Burp Suite to inspect what the server sends beyond the rendered HTML.

Intercepting the Request

I entered an arbitrary tracking number (gfhf) and submitted the form. Burp Suite intercepted the following request: GET /track?id=gfhf HTTP/2 Host: .challenges.webverselabs-pro.com The request is ordinary: a single query parameter and standard browser headers. The interesting part of this challenge is not in the request but in the response.

Response Analysis

I forwarded the request to Repeater and sent it. The response headers contained a non-standard custom header:

HTTP/2 200 OK Content-Type: text/html; charset=utf-8 Server: cloudflare X-Internal-Order-Ref: WEBVERSE{….} X-Frame-Options: DENY X-Content-Type-Options: nosniff

This header stands out for several reasons: —

It is not part of the standard HTTP header set; the X- prefix conventionally marks custom headers. — The other custom-looking headers (X-Frame-Options, X-Content-Type-Options) are well-known security headers, whereas X-Internal-Order-Ref is application-specific. — The word "Internal" indicates the value was intended for backend use and was never meant to reach the client.

Proof of Exploitation

The flag was returned directly in the X-Internal-Order-Ref response header. No exploitation beyond passive traffic inspection was required.

Flag: WEBVERSE{….}

Impact

Leaking internal values through response headers can expose:

• Internal identifiers and order references — Debug state and environment details Backend hostnames and infrastructure information — Tokens or session-related data, depending on what the debug code emits

Even when a single value looks harmless, such disclosures support reconnaissance and can be chained into more serious attacks

Root Cause

Debugging functionality (a custom response header) added during development was not removed before deployment. The release process did not include a review of response headers.

Mitigation

Remove all debug middleware and custom diagnostic headers from production builds.

Use environment-based configuration so debug features are disabled by default in production.

Include response header inspection in pre-release security reviews and automated tests.

Strip or filter unexpected outbound headers at the reverse proxy or gateway.

Key Takeaways

When the page reveals nothing, inspect the response headers. — Always look for non-standard headers such as X-Internal-, X-Debug, X-Backend- and X-Environment.

Check responses from multiple endpoints, not only the homepage; here the leak appeared on /track.

Classification

1. OWASP Top 10 (2021): A05, Security Misconfiguration
2. Weakness: CWE-200, Exposure of Sensitive Information to an Unauthorized Actor
3. Subtype: Debug header information disclosure

Written by 0xdzubair