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hunt-shadow-api skill

by elementalsouls·elementalsouls/Claude-BugHunter·4.7k stars·MIT

Hunt shadow / zombie / undocumented API surface (OWASP API9 Improper Inventory Management) — enumerate the full API version history (v1/v2/beta/legacy paths, header- and subdomain-based versioning), pull and diff every reachable OpenAPI/Swagger spec (including ones only findable via the Wayback Machine), and behaviorally diff old vs. current versions for auth/rate-limit/validation regressions rather than just response-shape differences. Distinct from hunt-api-misconfig, which owns exploitation once you have a spec or endpoint (mass assignment, JWT, OData, Swagger-chain attacks); distinct from hunt-subdomain, which owns host-level discovery. This skill owns the version-inventory and behavioral-diff workflow itself. Use when the target has versioned API paths, multiple specs, a changelog referencing deprecated endpoints, or a mobile app whose hardcoded backend calls look older than the current web app's.

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Install the hunt-shadow-api skill

A skill is a folder. Copy it into your agent's skills folder and the agent loads it when the task matches its description. 

git clone --depth 1 https://github.com/elementalsouls/Claude-BugHunter.git /tmp/Claude-BugHunter
mkdir -p ~/.claude/skills
cp -r /tmp/Claude-BugHunter/skills/hunt-shadow-api ~/.claude/skills/hunt-shadow-api
available in every project

In the Claude apps, zip the folder and upload it from the Skills settings. The folder on GitHub

The instructions your agent would load

SKILL.md as published, without the frontmatter. Read it on GitHub

OWASP API9 — Improper Inventory Management (Shadow / Zombie APIs)

As an API evolves, old versions and internal/staging routes routinely stay reachable without receiving the same security fixes as the current version — because nobody tracks that they still exist. The bug is rarely in one endpoint; it's in the delta between what an old version enforces and what the current version enforces on the same operation.

When to use

Trigger when:

headers are in play.

  • Versioned paths are visible (/v1/, /v2/, /api/2023-01-01/) or Accept/X-API-Version

that look like an older backend version than the current web app calls.

  • A changelog, release notes, or deprecation notice references removed/old API behavior.
  • A mobile APK/IPA (via apk-redteam-pipeline / ios-redteam-pipeline) hardcodes endpoints

exist.

  • Multiple OpenAPI/Swagger specs are discoverable, or info.version in one spec implies others

DO NOT use for single-version APIs with no version history — there's nothing to diff; go straight to hunt-api-misconfig for direct exploitation of the one surface that exists.

Stage 1 — Enumerate the Full Version Surface

# Path-based versioning
for v in v1 v2 v3 v4 beta alpha internal legacy old 2022-01-01 2023-01-01 2024-01-01; do
  curl -s -o /dev/null -w "%{http_code} /api/$v/\n" "https://$TARGET/api/$v/"
done

# Header-based versioning
curl -s -H "X-API-Version: 1" https://$TARGET/api/users
curl -s -H "Accept: application/vnd.company.v1+json" https://$TARGET/api/users

# Subdomain-based versioning
for sub in api api-v1 api-v2 apiv1 apiv2 legacy-api old-api internal-api staging-api; do
  curl -s -o /dev/null -w "%{http_code} $sub\n" "https://$sub.$TARGET/"
done

A 200/401/403 on an old version path (anything but 404/connection-refused) means the version is still live and worth carrying into Stage 3, even if it demands auth.

Stage 2 — Pull Every Reachable Spec, Not Just the Linked One

for path in openapi.json swagger.json v1/swagger.json v2/swagger.json v3/api-docs \
            api-docs.json swagger/v1/swagger.json .well-known/openapi.json; do
  curl -s -o /dev/null -w "%{http_code} /$path\n" "https://$TARGET/$path"
done

# Wayback Machine — a DEPRECATED version's spec often stays indexed after the live link is removed
curl -s "http://web.archive.org/cdx/search/cdx?url=$TARGET/*swagger*&output=json&collapse=urlkey"
curl -s "http://web.archive.org/cdx/search/cdx?url=$TARGET/*openapi*&output=json&collapse=urlkey"

When more than one spec resolves (a current one and an archived/old one), diff the endpoint inventories directly:

jq -r '.paths | keys[]' v1-swagger.json | sort > /tmp/v1_paths.txt
jq -r '.paths | keys[]' v2-swagger.json | sort > /tmp/v2_paths.txt
comm -23 /tmp/v1_paths.txt /tmp/v2_paths.txt   # in v1 only — candidates for "still live but forgotten"

For every path in that diff, confirm it's still reachable against the v1 base URL. A route documented only in the old spec that still returns something other than 404 is a zombie- endpoint candidate — carry it into Stage 3.

Stage 3 — Behavioral Diff Between Old and Current Version

For each operation that exists in both versions, compare security-relevant behavior, not response shape. Response shape differences are Informational; behavioral security regressions are the finding.

privilege token that the current version rejects?

  • Auth strength. Does the old version accept no token, an expired token, or a lower-
curl -s -H "Authorization: Bearer $EXPIRED_TOKEN" https://$TARGET/api/v1/users/me -w '\n%{http_code}\n'
  curl -s -H "Authorization: Bearer $EXPIRED_TOKEN" https://$TARGET/api/v2/users/me -w '\n%{http_code}\n'

endpoint; a missing 429 on the old version means rate-limiting was added later and never backported.

  • Rate limiting. Burst the same number of requests against both versions' equivalent

old version accepting what the new one rejects means hardening happened forward-only — chain into whichever injection class the payload targets (hunt-sqli, hunt-idor, etc.).

  • Input validation. Send the identical injection/oversized/malformed payload to both; the

users' data, internal notes, PII — that the current version has since redacted?

  • Field exposure. Does the old version's response body include fields — internal IDs, other

Stage 4 — Deprecated / Internal Routes Never Referenced by the Current UI

/_internal/, /test/, /staging/) — reuse hunt-source-leak's JS-bundle grep patterns for this specifically.

  • Grep JS bundles for API calls no visible UI flow triggers (/internal/, /admin/, /debug/,

often reference an older backend version than the current web app calls. Treat every APK/IPA-sourced endpoint as a version-diff candidate against the live web API.

  • Check robots.txt / sitemap.xml for disallowed API paths — a self-inflicted disclosure.
  • Mobile-app endpoint inventories (via apk-redteam-pipeline / ios-redteam-pipeline) very

False-Positive Gate

Informational. The finding is a security-relevant regression — auth, rate-limit, or validation that got weaker going backward in version history.

  • A version difference alone (different response shape, cosmetic field renaming) is

claiming a behavioral difference — send a payload that would actually behave differently under old vs. new logic, not just compare a version string in the response body.

  • Confirm the old endpoint is not simply an alias/proxy to the current implementation before

is not a finding — confirm the underlying operation still executes.

  • A 200 on a path that just serves a static "this API version is deprecated, use v2" message

Severity Table

Related Skills & Chains

assignment, JWT attacks, OData, Swagger-chain attacks). This skill hands it a sharper target: "here's a zombie endpoint with weaker validation than the current one."

  • hunt-api-misconfig — owns exploitation once a spec or endpoint is in hand (mass

host, potential takeover). This skill owns what happens once you're inside a given host's version surface.

  • hunt-subdomain — owns host/subdomain-level discovery (api-v1.target.com as its own

specifically for version-diffing rather than secret extraction.

  • hunt-source-leak — JS-bundle grep for internal/undocumented calls; reused here

older API version; every mobile-sourced endpoint is a version-diff candidate.

  • apk-redteam-pipeline / ios-redteam-pipeline — mobile builds routinely hardcode an

chained to actual brute-forceable impact (login, OTP, enumeration).

  • hunt-brute-force — a rate-limit regression found here is only a complete finding once

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