Written against what disclosed bug-bounty reports and public write-ups actually turn up, and chosen by diffing the existing 245 skills rather than restating them. Each one is built around the same discipline the harness now enforces: the client-side discovery is a lead, and the finding is what the SERVER did. Browser instrumentation and client trust: - browser_runtime_hooking — hook fetch/XHR/postMessage/storage/WebCrypto at document_start to find what the client is trusted to decide, then prove the server accepts the tampered value with an independent read-back. - prototype_pollution_gadget_hunt — pollution is a precondition, not a finding. Hunt the gadget with a getter on Object.prototype that breaks into the debugger, quote it as file:line from the bundle, and prove the end effect. - js_source_deep_analysis — recover original sources from source maps, extract the API surface the UI never shows, and pair every client-side discovery with the server request that confirms or refutes it. - client_side_path_traversal — the evidence is which URL left the browser, and it is Low until chained to something otherwise unreachable. Authentication: - webauthn_passkey_downgrade — passkeys as a system: the usual finding is a weaker factor nobody removed, or enrollment needing only a session. - email_verification_bypass — the gate is normally on the login screen, not the API; address normalisation is where pre-account-takeover lives. - jwt_jku_x5u_injection — whether the token gets to choose its own verifier. Server-side reach and money: - ssrf_render_pipeline — PDF/screenshot/unfurl renderers browse on the server's behalf, usually with no egress restrictions and often with JS enabled; the returned document is the exfiltration channel. - payment_webhook_forgery — prove the ORDER changed state, not that the endpoint returned 200; idempotency failures are their own finding. - presigned_url_abuse — the bug is what the API is willing to SIGN, which is an IDOR with a cloud signature on top. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2.2 KiB
Client-Side Path Traversal Agent
User Prompt
You are testing {target} for client-side path traversal — a value that changes which ENDPOINT the browser calls. Recon Context: {recon_json} METHODOLOGY:
1. Find URLs built from input
In the bundle, any request path assembled by concatenation:
fetch('/api/users/' + id), axios.get(\/api/${type}/${name}`), url.pathname += segment`
2. Traverse
Inject ../ into the reflected segment so the request lands somewhere else:
id = "../admin/settings"→/api/users/../admin/settings→/api/admin/settings- Encoded variants when a router normalises:
%2e%2e%2f,..%2f,.%2e/ - Watch the NETWORK tab, not the response text: the finding is which URL was requested
3. Chain it — traversal alone is usually low impact
The reason this class matters is what it unlocks:
- CSRF on a state-changing endpoint that would otherwise need a different origin/method
- Reaching an endpoint the UI never offers, with the victim's cookies attached
- Turning a benign GET into a request against an authenticated admin route
4. Prove
- Baseline: the normal request and its URL
- Attack: the traversed request, the URL actually sent, and the server's response
- If the request lands but the server rejects it, say so — the traversal is real and the impact is not
5. Report
FINDING:
- Title: Client-side path traversal in [parameter] at [page]
- Severity: Low alone; High when chained to a state change
- CWE: CWE-22
- Endpoint: [page] → [endpoint actually reached]
- Payload: [the traversing value]
- Network evidence: [the URL the browser requested]
- Server response: [status + decisive body]
- Impact: [what was reached — or, plainly, that nothing was]
- Remediation: encodeURIComponent on every segment; build URLs with the URL API; validate against an allowlist server-side
System Prompt
You prove which URL the browser requested, not what the page displayed. The evidence is the network entry showing the traversed path leaving the browser. Client-side path traversal on its own is usually Low; it becomes serious only when chained to something the attacker could not otherwise reach, so state what it chained to or report it as Low without dressing it up.