Writing Vuln Reports

Writing vulnerability reports

A finding that isn't clearly reported doesn't get fixed. The job of a report is to move a specific defect from your head into the maintainer's, with enough proof that they can reproduce it in minutes and enough impact that they prioritize it, and nothing else. This skill turns a schema-shaped finding into that report.

When to use

• A finding is confirmed (see FINDING-SCHEMA.md) and you're writing it up for a human: bounty submission, advisory, ticket, email.
• You have several findings and need consistent, triager-friendly writeups.

Scope check

Only report findings from authorized testing, to the party entitled to receive them (the program's channel, the maintainer's security contact, your client). Don't disclose someone else's data or a third party's system you weren't scoped to touch. When in doubt about the channel, ask before sending - a report is outward-facing and hard to unsend.

The structure that gets findings fixed

Lead with impact, prove it fast, make the fix obvious. Sections:

1. Title - the specific defect and where. "IDOR in admin_bulk_delete lets any user delete any post," not "Access control issue."
2. Summary (2 to 3 sentences) - what the bug is, who can trigger it, what they get. A busy triager should grasp severity from this alone.
3. Impact - the concrete consequence, tied to the target's threat model. Who is harmed, what they lose, what precondition is needed (auth level, timing, config). Don't inflate; don't undersell.
4. Steps to reproduce - numbered, exact, copy-pasteable. Real request(s) with method, path, headers that matter, and body. State the starting state (logged in as user A, two accounts, a seeded record). A stranger must reproduce it from these steps alone.
5. Proof - the request/response pair (or crash/log) that shows it firing. Redact secrets and unrelated PII. For whitebox findings, include the source→sink path and the decisive code excerpt from the schema's evidence.
6. Root cause - the actual defect, at the decisive hop (the missing check, the unbounded copy, the non-atomic act). One or two sentences.
7. Remediation - the fix at that hop, plus the general pattern ("parameterize the query," "resolve against base and reject escapes," "atomic conditional update"). Offer the fix; don't demand a specific patch.
8. Severity - a rating with the reasoning. If the program uses CVSS, give the vector and score; otherwise a justified low/med/high/critical. The reasoning matters more than the number.
9. References (optional) - CWE id, relevant advisory, similar prior fixes.

From schema to report

The finding schema already holds most of this. Map it: title→title; source+sink+impact→summary/impact; path+evidence→reproduction/proof; kill_reason never ships (killed findings aren't reported); remediation→ remediation; severity→severity; commit→pin the "affected version." If a field is thin, that's a signal the finding isn't report-ready - go back and fill it, don't paper over it.

Reproduction is the report

Most rejected or slow-triaged reports fail here. Rules:

• Reproduce it yourself from your own written steps, in a clean state, before sending. If your steps don't reproduce for you, they won't for them.
• Minimize. Strip every step and header that isn't load-bearing. The shortest path that still fires is the best path.
• Make preconditions explicit. "Two accounts," "a coupon that hasn't been redeemed," "run the two requests concurrently." Hidden state is the #1 reason a triager can't reproduce.
• Show, don't assert. "Returns 200 with user B's record" beats "it's vulnerable."

Worked example (outline)

Title: IDOR in POST /api/reports/export - filename allows arbitrary file write Summary: An authenticated user can set export.filename to an absolute or traversal path; the server writes the export there, overwriting arbitrary files the service can write. Impact: Arbitrary file write as the service account → RCE by dropping a cron/config file. Precondition: any authenticated account. Steps: 1. Log in as any user. 2. POST /api/reports/export with body {"filename":"../../../../etc/cron.d/x", ...}. 3. Observe the file written outside the export dir. Proof: [request/response], plus source path handler.export_report → ReportJob → export_writer.write → open() with the unchecked filename. Root cause: filename is used to build the output path with no normalization or base-containment check. Remediation: Resolve the path against the export base and reject if it escapes; or ignore client filenames and generate one. Severity: High (CVSS vector + reasoning).

Rationalizations to reject

• "They'll figure out the repro." → They won't; they'll close it. You reproduce it from your own steps first.
• "Bigger impact wording = higher payout." → Inflation gets you dinged and distrusted. Rate it honestly; let the facts carry it.
• "I'll include the whole capture/log." → Minimize and redact. Noise buries the bug and can leak PII.
• "One report, many bugs." → One defect per report unless the program says otherwise; bundled reports get partially triaged and partially lost.

Related

• FINDING-SCHEMA.md - the source record every report is built from.
• adjudicating-taint-paths, auditing-guard-gaps, detecting-memory-safety-bugs, detecting-race-conditions - where confirmed findings come from.