Executive brief
OpenSign is an open-source document signing platform used for handling contract signatures and approvals. When one-time password (OTP) verification is disabled, the getDocument cloud function fails to validate user identity, allowing attackers to retrieve complete document details including all signers' information and valid download tokens using only a document ID from a guest signing link. This exposes sensitive business documents and signer information without requiring any authentication.
Technical details
The vulnerability is an authentication bypass in the getDocument cloud function (Parse cloud function). The root cause is improper conditional logic: when IsEnableOTP is false, the function returns the full document without any access control checks, whereas it should validate caller identity regardless of OTP settings. The attack vector is network-based and requires no authentication—an attacker with knowledge of a document identifier (obtainable from a guest signing link) can call the function directly to retrieve all document metadata, signer details, sender identity, and download tokens. The fix is to apply consistent access control validation regardless of OTP enablement status.
Affected products
- OpenSign OpenSign through 2.41.3
Timeline
- 2026-09-16: disclosed