The macOS High Sierra 10.13.2 update improves the stability, compatibility and security of your Mac, and is recommended for all users. This update:. Improves compatibility with certain third-party USB audio devices. Improves VoiceOver navigation when viewing PDF documents in Preview. Improves compatibility of Braille displays with Mail. Previously, in OS X El Capitan, users had the option to change the Mac Gatekeeper preferences to “Allow apps from Anywhere“. However, macOS Sierra changed this. You now only have the options to either allow apps from the App Store, or from the App Store and Identified Developers. OS X El Capitan (top) vs macOS Sierra (bottom).

High Sierra Gatekeeper Anywhere Login
High Sierra Gatekeeper Anywhere Remote
High Sierra Gatekeeper Anywhere Access
High Sierra Gatekeeper Anywhere Download

Advanced Mac users may wish to allow a third option, which is the ability to open and allow apps downloaded from anywhere in MacOS Catalina, macOS Sierra, macOS High Sierra, and MacOS Mojave. To be clear, the “Allow applications downloaded from anywhere” option is hidden by default in Gatekeeper for macOS from Sierra onward.
Accounts, Security & Gatekeeper. In an era when security is the hottest high-tech buzzword, Apple was smart to make security a focal point for macOS. It was already virus-free and better protected from Internet attacks than Windows. But macOS High Sierra is the most impenetrable Mac system yet, filled with new defenses against the dark arts.
You’ll now be able to open and launch apps from anywhere under Mac High Sierra, but be forewarned this turns off Gatekeeper and is not recommended for the vast majority of Mac users.

Gatekeeper
Developer(s)	Apple Inc.
Initial release	July 25, 2012
Operating system	macOS

Gatekeeper is a security feature of the macOSoperating system by Apple.^[1]^[2] It enforces code signing and verifies downloaded applications before allowing them to run, thereby reducing the likelihood of inadvertently executing malware. Gatekeeper builds upon File Quarantine, which was introduced in Mac OS X Leopard and expanded in Mac OS X Snow Leopard.^[3]^[4] The feature originated in version 10.7.3 of Mac OS X Lion as the command-line utilityspctl.^[5]^[6] A graphical user interface was added in OS X Mountain Lion and later also in version 10.7.5 of Lion.^[7]

Functions[edit]

Configuration[edit]

Gatekeeper options in the System Preferences application. Since macOS Sierra, the 'Anywhere' option is hidden by default.

In the security & privacy panel of System Preferences, the user has three options:

Mac App Store: Allows only applications downloaded from the Mac App Store to be launched.
Mac App Store and identified developers: Allows applications downloaded from the Mac App Store and applications signed by certified Apple developers to be launched. This is the default setting since Mountain Lion.
Anywhere: Allows all applications to be launched. This effectively turns Gatekeeper off. This is the default setting in Lion. Since macOS Sierra, this option is hidden by default.^[8]^[9]; However, this option can be re-enabled by using the 'sudo spctl --master-disable' command from the Terminal and authenticating with an admin password.

The command-line utility spctl provides granular controls, such as custom rules and individual or blanket permissions, as well as an option to turn Gatekeeper off.^[6]

Quarantine[edit]

Upon download of an application, a particular extended file attribute ('quarantine flag') can be added to the downloaded file.^[10] This attribute is added by the application that downloads the file, such as a web browser or email client, but is not usually added by common BitTorrent client software, such as Transmission, and application developers will need to implement this feature into their applications and is not implemented by the system. The system can also force this behavior upon individual applications using a signature-based system named Xprotect.^[11]

Execution[edit]

Screenshot of a system alert that appears when Gatekeeper prevents an application from running, because it was not signed by an Apple certified developer.

When the user attempts to open an application with such an attribute, the system will postpone the execution and verify whether it is:

blacklisted,
code-signed by Apple or a certified developer,
the code-signed contents still match the signature.

Since Mac OS X Snow Leopard, the system keeps two blacklists to identify known malware or insecure software. The blacklists are updated periodically. If the application is blacklisted, then File Quarantine will refuse to open it and recommend to the user to move it to trash.^[11]^[12]

Gatekeeper will refuse to open the application if the code-signing requirements are not met. Apple can revoke the developer's certificate with which the application was signed and prevent further distribution.^[1]^[3]

Once an application has passed File Quarantine or Gatekeeper, it will be allowed to run normally and will not be verified again.^[1]^[3]

Override[edit]

To override Gatekeeper, the user (acting as an administrator) either has to switch to a more lenient policy from the security & privacy panel of System Preferences or authorize a manual override for a particular application, either by opening the application from the context menu or by adding it with spctl.^[1]

Path randomization[edit]

Developers can sign disk images that can be verified as a unit by the system. In macOS Sierra, this allows developers to guarantee the integrity of all bundled files and prevent attackers from infecting and subsequently redistributing them. In addition, 'path randomization' executes application bundles from a random, hidden path and prevents them from accessing external files relative to their location. This feature is turned off if the application bundle originated from a signed installer package or disk image or if the user manually moved the application without any other files to another directory.^[8]

Implications[edit]

The effectiveness and rationale of Gatekeeper in combating malware have been acknowledged,^[3] but been met with reservations. Security researcher Chris Miller noted that Gatekeeper will verify the developer certificate and consult the known-malware list only when the application is first opened. Malware that already passed Gatekeeper will not be stopped.^[13] In addition, Gatekeeper will only verify applications that have the quarantine flag. As this flag is added by other applications and not by the system, any neglect or failure to do so does not trigger Gatekeeper. According to security blogger Thomas Reed, BitTorrent clients are frequent offenders of this. The flag is also not added if the application came from a different source, like network shares and USB flash drives.^[10]^[13] Questions have also been raised about the registration process to acquire a developer certificate and the prospect of certificate theft.^[14]

In September 2015, security researcher Patrick Wardle wrote about another shortcoming that concerns applications that are distributed with external files, such as libraries or even HTML files that can contain JavaScript.^[8] An attacker can manipulate those files and through them exploit a vulnerability in the signed application. The application and its external files can then be redistributed, while leaving the original signature of the application bundle itself intact. As Gatekeeper does not verify

High Sierra Gatekeeper Anywhere