Duplicate JSON Keys
A10 · ≈ 40 min · 0 solves
Explore the application as a real target: map the exposed functionality, inspect requests and responses, build a working exploit, and recover the rotating flag. If you get stuck, the verified official solution is available below as an optional spoiler.
Rules of engagement
Stay inside the generated lab URL. Use only the synthetic accounts and data in this instance. The main SecOne4all site and external systems are out of scope.
Challenge brief
What counts as a valid solve
Gateway and application parsers choose different values from duplicate JSON keys.
POST /duplicate.
trigger the exceptional path and demonstrate its unsafe fallback or partial state; the successful workflow returns the current rotating flag.
Work only inside your generated lab URL and submit the flag within 40 minutes.
Official solution
Contains the complete exploitation path. Open it only when you want the spoiler.
Reveal official solutionStep-by-step · verified against the live lab
Official solution · A10 · Duplicate JSON Keys
Objective
Gateway and application parsers choose different values from duplicate JSON keys.
Steps
- Start the isolated lab and establish the normal response or state.
- Prepare the smallest input that triggers the timeout, parser, arithmetic, retry, or cleanup edge case.
- Trigger and exploit the exceptional path: POST raw JSON
{"role":"user","role":"admin"}to/duplicate. - Confirm the unsafe fallback or partial state returns the rotating flag.
- Submit the flag before stopping the lab.
Expected proof
A successful response for duplicate-json-key-parser returns the instance-specific rotating flag. The flag is valid only for the current player and running instance.
Safety boundary
Use only the generated lab URL. No request to the main site, another user, or an external service is part of this solution.