Component: finbot/mcp/servers/finstripe/server.py → create_transfer
Root cause:

# vendor_account is a free-form string, never compared to vendor.bank_account_number
txn = repo.create_transaction(..., vendor_account=vendor_account, ...)

Steps to reproduce:

1. Create vendor with bank_account_number='123456789012'
2. Call create_transfer(vendor_account='999999999999')

Expected Behavior: error — vendor_account mismatch
Actual Behavior: transfer created to arbitrary account

How to execute:

pytest tests/unit/mcp/test_finstripe.py::TestCreateTransferValidation::test_mcp_create_011_arbitrary_vendor_account_accepted -v

Impact: Attacker redirects payments to any account via prompt injection targeting the vendor_account argument.

Acceptance criteria:

• TestCreateTransferValidation::test_mcp_create_011_arbitrary_vendor_account_accepted pass