Payload Plugins is a collection of plugins designed to enhance Payload CMS. From 0.3.0 until 0.4.0, @jhb.software/payload-cloudinary-plugin deployments with clientUploads enabled expose POST /api/cloudinary-generate-signature, whose handler in cloudinary/src/getGenerateSignature.ts passes attacker-controlled body.paramsToSign directly to cloudinary.utils.api_sign_request without a key allowlist, collection policy, timestamp freshness check, or configured-folder enforcement. Any authenticated Payload user can obtain a valid Cloudinary HMAC-SHA1 signature for unauthorized parameters such as overwrite, type, notification_url, invalidate, folder, and public_id. The signature can authorize asset replacement, upload visibility changes, callbacks to attacker-selected URLs, cache invalidation, and uploads outside the intended folder. The client-visible Cloudinary API key is expected by the upload design, but the unrestricted server-side signature supplies the authorization value needed to complete these operations. This vulnerability is fixed in 0.4.0.

Affected: npm: @jhb.software/payload-cloudinary-plugin

## Arbitrary Cloudinary API Parameter Signing in @jhb.software/payload-cloudinary-plugin

### Summary

`@jhb.software/payload-cloudinary-plugin` v0.3.4 exposes a server-side signing endpoint (`POST /api/cloudinary-generate-signature`) that passes attacker-supplied `paramsToSign` directly to `cloudinary.utils.api_sign_request()` without any allowlist, key filtering, or policy enforcement. Any authenticated Payload user can obtain a cryptographically valid Cloudinary HMAC-SHA1 signature for arbitrary upload parameters — including `overwrite=true`, `type=private`, `notification_url`, and path-traversal folder values — enabling unauthorized asset replacement, access-control bypass, and potential SSRF within the configured Cloudinary account.

### Details

When `clientUploads: true` is configured, the plugin registers a signing handler at `cloudinary/src/index.ts:74-79`. The handler is implemented in `cloudinary/src/getGenerateSignature.ts`.

**Vulnerable code path (step by step):**

1. `cloudinary/src/index.ts:58` — `initClientUploads` registers the server upload handler. 2. `cloudinary/src/index.ts:68` — The Cloudinary API key is exposed to client handler props by design. 3. `cloudinary/src/index.ts:74-79` — The signing endpoint is mounted at `/cloudinary-generate-signature`. 4. `cloudinary/src/getGenerateSignature.ts:18` — The default access control checks only `!!req.user`, permitting any authenticated user. 5. `cloudinary/src/getGenerateSignature.ts:46` — The entire request…