[dxd]

I think it means that this exploit has been possible since the application was made, the zeroth day.

[efdee]

It doesn't. Technically, zero-day in the context of exploits means the exploit was circulating and/or being used before the authors of the attacked piece of software were made aware of the vulnerability (or before the vulnerability was made public, or before the day a patch was made available, depending on who you ask).