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adversarial-verification

Testing & Quality
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Systematically probe a modernized Next.js application for logic flaws, security vulnerabilities, or missing features. Use this to find bugs or cases where the migration failed to match legacy behavior.

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How to use this skill

Bring this guide into your coding agent with a prompt tailored to the tool you use.

  1. Open your project in Codex.
  2. Copy the prompt below and paste it into your agent.
  3. Review the proposed files and risks before you approve installation.
Prompt to paste
I want to install this Agent Skill for this project in Codex.

Source SKILL.md: https://github.com/GoogleCloudPlatform/devrel-demos/blob/HEAD/other/modernizing-expressjs/.agents/skills/adversarial-verification/SKILL.md

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Copying this prompt does not install or run the skill. Review third-party files before use. Codex skill guide

Adversarial Verification

Take the role of an "Adversary" to scrutinize the modernized application. Proactively search for logic flaws, security vulnerabilities, and functional regressions that traditional tests may have missed.

Objective

Identify where the modernization is "broken" or "insecure." The goal is to maximize the surface area for finding errors by stress-testing authorization, validation, and data integrity.

Instructions for the Audit Subagent

Copy this checklist and track your progress:

Task Progress:
- [ ] Step 1: Authorization & Privilege Probes
- [ ] Step 2: Validation Stress-Testing
- [ ] Step 3: Data Integrity & "Dirty Data" Scrutiny
- [ ] Step 4: UI/UX Edge Case Exploration
- [ ] Step 5: Adversarial Audit Report

Step 1. Authorization & Privilege Probes

Attempt to bypass access controls to prove the new implementation is at least as secure as the legacy model:

  • Unauthenticated Access: Try to access protected interaction routes (POST/PUT/DELETE) without a valid session.
  • Vertical Privilege Escalation: Attempt to perform administrative actions from a regular user account.
  • Horizontal Privilege Escalation (IDOR): Try to modify or delete a resource (e.g., User, Post, Profile) that belongs to a different user. Ensure the "Ownership Guard" is strictly enforced.

Step 2. Validation Stress-Testing

Pressure the Zod schemas and Route Handlers with malformed input:

  • Schema Boundaries: Send empty strings for required fields, exceed character limits, or provide invalid formats (e.g., malformed emails or non-numeric IDs).
  • Malformed Payloads: Submit invalid JSON, excessively large payloads, or incorrect types (e.g., an array where a string is expected) to Route Handlers.
  • Response Consistency: Verify that validation failures return a consistent 422 Unprocessable Entity or 400 Bad Request as documented in API_Contracts.md.

Step 3. Data Integrity & "Dirty Data" Scrutiny

Investigate how the modernized app handles inconsistent or incomplete legacy data:

  • Null Reference Handling: Check how the UI and API behave when a referenced entity (e.g., a Comment's Author) is missing from the database.
  • Inconsistent Keys: Test the app against legacy records that may lack "required" fields introduced in the new Zod schemas. Does the app provide defaults or crash?

Step 4. UI/UX Edge Case Exploration

Identify regressions in the user experience compared to the legacy intent:

  • Error Feedback: Trigger validation errors and ensure the user receives clear feedback (e.g., Toasts or Form error messages).
  • Empty States: Verify that every resource list (index pages, sub-resource feeds) has a clean, helpful empty state (not just a blank screen).
  • Mobile Resiliency: Ensure the new ShadCN layout remains functional on small/narrow viewports.

Step 5. Adversarial Audit Report

Generate a docs/verification/Adversarial_Audit_Report.md. Categorize findings as:

  • Critical Security Flaws: Vulnerabilities like IDOR or session leaks.
  • Validation Oversights: Missing field checks or incorrect Zod rules.
  • Functional Deficiencies: Features that behave differently than the legacy intent.
  • UI Regressions: Broken layouts or missing user feedback.