Documenso's sign-field-with-token.ts, used by the live document-signing UI, allows a recipient with the ASSISTANT role to fetch and complete fields belonging to any later-or-equal-order, not-yet-signed recipient in the same envelope, with no restriction on field type. A newer V2 signing path (sign-envelope-field.ts) explicitly blocks assistants from completing SIGNATURE fields, and the project's own test suite comments confirm this guard is absent from the V1 path used here.

Documenso's sign-field-with-token.ts, used by the live document-signing UI, allows a recipient with the ASSISTANT role to fetch and complete fields belonging to any later-or-equal-order, not-yet-signed recipient in the same envelope, with no restriction on field type. The handler upserts a Signature record tied to the target field's recipientId with no check that field.type is SIGNATURE and the acting recipient owns it. A newer V2 signing path (sign-envelope-field.ts) explicitly blocks assistants from completing SIGNATURE fields, and the project's own test suite comments confirm this guard is absent from the V1 path used here. In a sequential-signing document, an assistant recipient can therefore forge another signer's signature field.