Hunt Shadow API Skill for Claude

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:

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

headers are in play.

• 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

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

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

exist.

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.

• Auth strength. Does the old version accept no token, an expired token, or a lower-

privilege token that the current version rejects?

  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'

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

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

backported.

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

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.).

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

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

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

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

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

this specifically.

• 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

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.

False-Positive Gate

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

Informational. The finding is a security-relevant regression — auth, rate-limit, or

validation that got weaker going backward in version history.

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

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.

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

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

Severity Table

| Finding | Severity |

|---|---|

| Old version bypasses auth entirely where current version requires it | Critical |

| Old version missing rate-limit present on current version | Medium–High (chain via hunt-brute-force) |

| Old version leaks extra fields (PII, internal IDs) vs. current | Medium–High |

| Old version accepts payloads the current version now validates/sanitizes | High (chain to the underlying injection class) |

| Version is reachable but behaviorally identical to current | Informational |

Related Skills & Chains

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

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

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

version surface.

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

specifically for version-diffing rather than secret extraction.

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

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

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

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