And here we are with a few spare minutes! My baby girl is a little cute devil who, like me, isn’t very found of sleeping all the time. She’s taking a lot of my attention so mom can rest. Well, it’s time well spent while I still have lots of it. Let’s get back to business… There was some fuss around with the latest version of the so called Flashback.C OS X Trojan....
I am a sucker for all OS X anti-debug promises I can find. There are so few tricks available that I am always curious to see if there is something new in town. So I started poking around Sentinel HASP Envelope for OS X to see what they use to fool my dear debuggers. Well, we have the usual ptrace and sysctl tricks, a check for a kernel debugger (via kernel boot arguments), and, to my (good) surprise, one of the anti-debug tricks I discovered a few months ago....
Dongles always had something mistique about them. Before this new age of packers, cryptors, etc, they were the top target to beat. In practice, that fame was only real in a reduced set of applications that correctly implemented the dongle. Most dongle-protected software feature bad implementations. Developers don’t spend enough time in this area or think that it’s the magic bullet to solve their problems. This program is another fine example of this problem....
I like things well done and the healthy discussion with snare about this topic remembered me this PoC was a bit incomplete. So I decided to close the missing gaps. The fix is pretty simple. Retrieve a new kauth credential with uid and gid equal to 0 and replace the old one (the code seems stable even without process locks). It also seems to work fine without the allproc lock. The backdoor also had a small “bug” that I didn’t noticed due to a coincidence....
While poking around OS X implementation of TrustedBSD to write the sandbox guide I had the idea of trying to abuse it for backdooring purposes. It’s kind of funny that something designed to protect can be so “easily” abused to install backdoors. This is not rocket science or a big breakthru post – I was just curious about the possibility to abuse the framework. You still need to find a way to install the kernel module!...