Ubuntu Security Notice 432-1 – Gerardo Richarte from Core Security Technologies discovered that when gnupg is used without –status-fd, there is no way to distinguish initial unsigned messages from a following signed message. An attacker could inject an unsigned message, which could fool the user into thinking the message was entirely signed by the original sender.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/54968/USN-432-1.txt
Source: https://packetstormsecurity.com/files/54968/Ubuntu-Security-Notice-432-1.html