Apple introduced Gatekeeper in 2012, creating it as a method of protection for users against malicious threats by adding various layers of security during installation of Mac apps. The feature is intended to ensure that apps users try to install on their Macs are legitimste and signed by a registered developer, minimizing the threat of malware. But now, a security researcher has discovered a simple method of bypassing Gatekeeper using a binary file already trusted by Apple to attack a user's computer (via Ars Technica).
Gatekeeper is meant solely to check the initial digital certificate when an app is downloaded on a Mac, ensuring that the program has been signed by an Apple-approved developer or at least comes from the Mac App Store itself before allowing the installation to proceed.
"If the application is valid—so it was signed by a developer ID or was (downloaded) from the Mac App Store—Gatekeeper basically says 'OK, I'm going to let this run,' and then Gatekeeper essentially exits," Patrick Wardle, director of research of security firm Synack, told Ars. "It doesn't monitor what that application is doing. If that application turns around and either loads or executes other content from the same directory... Gatekeeper does not examine those files."
Even if Gatekeeper is enhanced to its highest level of security settings, the new exploit can take advantage of a computer. Once the trusted file makes its way past the security program, it can then execute a handful of other malicious programs attached with the rest of the installation and gains the ability to install malicious software such as password-stealing programs, apps that can capture audio and video from a Mac's camera, and botnet software.
The researcher who discovered the exploit sent news of it to Apple about 60 days ago and "believes they are working on a way to fix the underlying cause or at least lessen the damage it can do to end users." Since then, an Apple spokesperson has confirmed the company is working on a patch for the issue and has asked that the identities of the specific files used in the exploit not be disclosed. Wardle plans to showcase his research on the Gatekeeper exploit at the Virus Bulletin Conference on Thursday in Prague.