I've only tested this with an iPhone 5s but I found what I would consider a security flaw. If passcode is on and you allow access to Siri when locked (General -> Passcode Lock), you can get pass the locked phone. You just hold the home button until Siri turns on. You tell Siri to launch an app. After the app opens, you hit the home button and you are on the homescreen without ever having to enter a passcode.
I would have thought that Siri's available actions would be limited from a locked phone.
I would have thought that Siri's available actions would be limited from a locked phone.