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    Harden Outbound URL Validation

    1

    Harden outbound URL validation against SSRF through schemes, userinfo, redirects, DNS/IP classification, IPv4/IPv6 forms, proxy resolution, rebinding windows, and destination revalidation.

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    Harden Outbound URL Validation

    Harden Outbound URL Validation

    Example session with this skill installed

    Our webhook tester blocks 127.0.0.1 and RFC1918 strings before sending, but it validates only hostname text and follows redirects automatically. Repair with a fake resolver/server while preserving the approved-host policy and timeouts.

    • Read your context and instructions
    • Compiled the harden outbound url

    Validation occurs on text before resolution and is not repeated on redirects. The repair parses once, applies scheme/port policy, resolves through an injectable resolver, classifies returned addresses, revalidates each redirect destination, and tests IPv6, numeric forms, redirects, and resolver changes.

    Connects securely to your tools. The creator never sees your data.

    About this skill

    The problem

    Inconsistent outbound URL validation leads to Server-Side Request Forgery (SSRF) vulnerabilities and unpredictable application behavior. Developers often struggle to align DNS resolution, host normalization, and redirect policies across fragmented codebases.

    What it does

    • Identifies every component involved in the outbound request lifecycle, from parsing to dispatch.
    • Patches URL parsers to handle host normalization and private/reserved IP classification correctly.
    • Enforces strict trust boundaries by moving validation before irreversible side effects or mutations.
    • Implements deterministic local fixtures and loopback endpoints for reliable regression testing.
    • Ensures retries, timeouts, and cleanup logic are bound to the specific transaction state.

    Why this beats prompting it yourself

    Generic prompts often suggest broad regex or simple blacklists that bypass edge cases like DNS rebinding or malformed userinfo. This skill systematically maps state ownership and authority boundaries to ensure security policies are actually enforceable in your specific architecture.

    Use cases

    • Hardening a proxy service against DNS rebinding and internal IP access.
    • Refactoring legacy request handlers to support unified SSRF-resistant validation.
    • Adding redacted observability and deterministic tests to outbound network modules.
    • Synchronizing redirect and proxy policies across multiple internal services.

    Known limitations

    This skill operates strictly on repository files and local fixtures. It cannot contact production services, read live secrets, or mutate deployed infrastructure.

    Find more skills like this on the Claude Skills Marketplace, the Codex Skills Marketplace and the Gemini Skills Marketplace, or browse Claude Skills for Security.

    Cannot redesign approved destination policy, proxy policy, redirect policy, DNS policy, timeout/retry policy, and public errors; cannot verify production infrastructure or prove every runtime, proxy, network, filesystem, or scheduler ordering.

    How to use

    1. 1

      Connect your agent to the Agensi MCP

      Copy the prompt and paste it into Claude, ChatGPT, Cursor or any agent that supports MCP. It sets up the connection for you. Manual setup

    2. 2

      Sign in to Agensi

      Your agent shows a sign-in link. Sign in and click Allow.

    3. 3

      Ask for what you need

      Your agent loads this skill and uses it on your task. It always asks before buying a skill.

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    Recently published to Agensi

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    Trust & safety

    Security scan

    Security scan passed 2 months ago

    Permissions

    Terminal / Shell
    Read Files
    Write Files

    Run on a clean branch with repository files and disposable local fixtures. Review patches and validation before merge. Keep production services, real credentials, customer payloads, and deployment out of scope.

    Listed2 months ago
    Updated9 days ago

    What's inside

    Frequently Asked Questions

    This skill implements a multi-layered defense-in-depth approach, addressing complex bypasses like DNS rebinding, malformed userinfo, and redirect loops that basic regex-based validation often misses.

    The skill is designed to integrate with codebases using standard HTTP libraries (such as Axios, Fetch, or Requests) and works within the environment of major AI coding assistants and IDE-based agents.

    You receive the modular validation logic, a suite of deterministic regression tests, and a configuration blueprint for setting up secure loopback endpoints and proxy policies.

    No, the skill operates entirely on your local source code and fixtures; it does not require access to your production environment, live API keys, or active network traffic.

    Yes, the skill is designed to identify and synchronize outbound policies across fragmented microservices, ensuring consistent redirect and IP classification logic across your entire architecture.

    New in Security