New Attack Bypasses Mac OS X Gatekeeper

msm1267 writes: Mac OS X's Gatekeeper security service is supposed to protect Apple computers from executing code that's not signed by Apple or downloaded from its App Store. A researcher, however, has built an exploit that uses a signed binary to execute malicious code. Patrick Wardle, a longtime Apple hacker, said Gatekeeper performs only an initial check on an application to determine whether it came from an untrusted source and should not be executed. Using a signed binary that passes the initial check and then loads a malicious library or app from the same or relative directory, however, will get an advanced attacker onto an OS X machine. Wardle disclosed his research and proof of concept to Apple, which said it is working on a patch, and may push out a short-term mitigation in the meantime.

Comments

There's an even greater flaw here.

[DejectedAngel]

OSX only checks the verification of the app if it sees that it is downloaded from a nonlocal source. If you download an unverified application, view package contents, and copy the files within to another folder and rename it with the .app extension, you can open anything! No admin rights required unless it requires an install!

Gatekeeper

[soft_guy]

If a user doesn't know how and can't figure out or google how to bypass Gatekeeper, they shouldn't be bypassing Gatekeeper. I'm a Mac developer and I work on a commercial application that uses a privileged helper tool which the app loads using SMJobBless and that tool is managed by launchd and executed as root. We are an identified developer and we sign our app as such. We don't distribute via the App Store and we are about to ship a new version that adds a kernel extension that I wrote. In recent versions of MacOS X, kernel extensions must be signed and they have to at least by signed by an identified developer who has applied for a kernel extension signing certificate. One of the scenarios that I pay attention to as far as security goes is that our daemon (aka "privileged helper tool") executes other processes and also controls the loading and unloading of our kernel extension. Most of those processes, and our kernel extension, are located in our application bundle. I wanted to avoid making dumb assumptions like that our application is running from a particular path, so the app communicates to the daemon via XPC and tells the daemon where the app bundle is located. The daemon doesn't just trust the app. It verifies that the app is code signed and that it is our app and that it hasn't been modified before it starts executing things or loading kernel extensions from inside the app bundle. I can easily imagine a scenario where an app could call our daemon and tell it some other location and cause us to execute malware if we didn't do this. Since I'm not a security expert, I constantly worry that someone will find a way to do this and I just hope we never become an attack vector. I do not want my product on Slashdot because of a security problem.