Documenso before 2.13.0 accepts PDF file uploads on the /api/files/upload-pdf endpoint without requiring authentication, session tokens, or API credentials. Unauthenticated attackers can upload arbitrary PDF files indefinitely to exhaust storage resources or fill the database with unlinked document records.

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.

A vulnerability was detected in Documenso up to 2.11.0. Affected by this vulnerability is an unknown functionality of the file packages/auth/server/lib/utils/handle-oauth-callback-url.ts of the component Google OAuth Login. The manipulation results in improper authentication. It is possible to launch the attack remotely. This attack is characterized by high complexity. The exploitation appears to be difficult. The exploit is now public and may be used. The pull request to fix this issue awaits acceptance.