Filing a HackerOne report

Drive a HackerOne vulnerability submission end to end: verify it's worth filing, write it up concisely, build a reproducible PoC with a video-ready README, fill the submission form in the browser, and hand the irreversible steps back to the user.

Non-negotiable safety rules

These are hard stops. They protect the user's account and their Signal.

1. Never enter credentials or 2FA codes. When the form gates on login, take a screenshot, tell the user to sign in themselves, and wait. Suggest they tick "Remember me for 2 weeks" (HackerOne sessions drop mid-flow otherwise).
2. Never click the final "Submit Report". It is an irreversible publish and it spends one of the user's reports. Fill everything, then hand off: the user reviews and submits. State this explicitly up front.
3. Never attach files the user didn't ask you to, and don't fabricate PoC output. The in-app browser can't drive the native file picker anyway - the user attaches the zip and the video.
4. Filing is per-user consent. Draft freely; the act of submitting is the user's.

Phase 0 - Dedup pre-flight (do this FIRST, every time)

The most expensive mistake is re-filing a finding the program already closed. It wastes a report and dents Signal. Before drafting anything:

• Search the local findings tree for prior work on the same root cause / sinks / code paths. Look especially in any duplicates/ folder and for filenames encoding a resolution: Informative-*, Duplicate-*, NA-*, Resolved-*. A file named Informative-1-<x>.md means the program already closed <x> as Informative.
• Compare code locations, not just titles. Grep both the candidate writeup and prior reports for the exact files/functions/sinks cited. If they overlap, it's the same finding regardless of new framing. (A "new vector" that strengthens the entry but reaches the same sink the program already judged is still a duplicate.)
• Offer to check the live program state: open HackerOne → My Reports, search a keyword from the finding, read the actual close reason/comment.
• If it's a dup: say so plainly and recommend not filing. Options: don't file; comment/appeal on the existing report instead of opening a new one; hold reports for something novel. Only proceed on the user's explicit go-ahead.
• Also surface program constraints visible on the submit page: "Trial Reports Remaining: N" and any Signal Requirement - a low Signal can block future submissions, so accuracy matters more than volume.

Phase 1 - Write the report (concise)

Use references/report-template.md. House style:

• Plain, direct, first person ("we found this field is forgeable"), not marketing prose.
• State each fact once. The same "new vector / defeated mitigation" point tends to sprawl across Summary, Component, Steps, and Impact - keep it in Summary + the Steps variant, and don't re-litigate it in Impact.
• No em dashes if the user prefers plain hyphens; use spaced hyphens - and split run-ons into sentences.
• Sections: Summary → Version/Affected → Component (vulnerable code paths) → Steps To Reproduce → Supporting Material → Impact → Suggested Fix.
• Title goes in its own field (max ~150 chars): <vuln type> via <mechanism> (<feature/component>, <version/context>). Don't repeat the title as the first line of the Description body.

Phase 2 - PoC package + video-ready README

Goal: a self-contained folder the triager can run and the user can film. Use references/poc-readme-template.md.

• One command per step, copy-paste, in order: prerequisites check → environment setup → baseline (the thing that is denied) → exploit → the money-shot success → a control that proves the mechanism → teardown.
• The money shot is a before/after: the same request denied, then succeeding, with only the exploited variable changed. That's what the video should capture.
• Actually run the exact README blocks on a clean environment before shipping. Repro commands that work in your head often fail copy-paste (auth/credential precedence, working-directory resets, tool flags that don't override config). Fix them until a fresh run reproduces.
• Prefer a few transparent commands over a big opaque .sh. If shared shell state is the only reason for a script, capture it in a tiny helper function inside the README instead.
• Ship: README.md (the walkthrough), the exploit inputs, an annotated pointer to the vulnerable source lines, a non-interactive runner, and any plumbing clearly labeled "not part of the vulnerability". Zip it; reference it in the report as poc.zip. The user records poc.mov and attaches both.

Phase 3 - Browser: reach the submission form

Use the in-app Browser (mcp__Claude_Browser__*) or Claude-in-Chrome. Gotchas learned:

• Navigate to hackerone.com/<program>. The submit entry is "Submit without Report Assistant" (full manual form). Its href looks like /<program>/reports/new?type=team&report_type=vulnerability.
• Do NOT deep-link that URL - it's a client-side SPA route and returns "Page not found" on direct navigation. Click the link on the program page instead.
• Expect a login/2FA gate → hand off to the user (safety rule 1). After they sign in, the program page may need a reload.
• Sessions expire mid-flow; if the form empties or bounces to sign-in, have the user re-auth with "Remember me".

Phase 4 - Fill the form

The manual form is a numbered flow. Prefer read_page refs over pixel coordinates (the pane rescales screenshots and raw-coordinate clicks miss). Use form_input for text fields - it's reliable.

After filling, offer to click Preview on the Markdown fields so the user can eyeball rendering. Verify the "Review and Submit" panel shows the right Title/Asset.

Phase 5 - Hand off

Summarize the filled state as a table (Asset / Weakness / Severity / Title / Description / Impact = done). List what remains and that it's the user's: attach zip, record+attach video, decide any judgment-call CVSS metric, review, click Submit. Re-state that you won't click Submit and won't loop on the blocked login.

References

• references/report-template.md - the concise finding writeup skeleton with all section headings.
• references/poc-readme-template.md - the video-ready copy-paste reproduction README pattern.