The glaring security hole in Docker is that it has not designed a solution for keeping secret data necessary to build an image from being in the image at run time.
They also haven't solved the general case of keeping transient build data out of the final image either, but that's a broader problem that doesn't necessarily involve security concerns.
For now not a lot of people are concerned about either problem so it's not getting the attention it deserves. But they've been steadily peppered with inquiries about these issues for a year or two now and they still don't have an answer, which is concerning. I believe this is one of the reasons the CoreOS guys wandered off to do their own thing.
Fortunately for us and unfortunately for them, they have the design aesthetics of the Marquis de Sade, and until they start giving even half a thought to ergonomics, Docker is perfectly safe.
They also haven't solved the general case of keeping transient build data out of the final image either, but that's a broader problem that doesn't necessarily involve security concerns.
For now not a lot of people are concerned about either problem so it's not getting the attention it deserves. But they've been steadily peppered with inquiries about these issues for a year or two now and they still don't have an answer, which is concerning. I believe this is one of the reasons the CoreOS guys wandered off to do their own thing.
Fortunately for us and unfortunately for them, they have the design aesthetics of the Marquis de Sade, and until they start giving even half a thought to ergonomics, Docker is perfectly safe.