- Researchers show Gatekeeper can be bypassed by replacing a previously run legitimate macOS app with malware
- Attack requires prior user‑level code execution, then swaps in a malicious app that Gatekeeper won’t re‑verify
- Apple dismissed the issue, saying locally rebuilt bundles fall outside Gatekeeper’s scope, leaving risk to social engineering
A pair of researchers claims to have found a way around Gatekeeper, a built-in macOS security feature that helps protect users from running malicious or untrusted software. However Apple doesn’t really see it that way and has seemingly decided not to pursue the issue further.
Gatekeeper’s modus operandi is rather simple - when a user downloads an app from outside the App Store, it verifies the product comes from an identified developer and is notarized by Apple. If it can’t verify it - it won’t allow it to run on the machine.
Now, security researchers Talal Haj Barky and Tommy Mysk claim that, as long as a legitimate app was run at least once on a macOS device, it can be replaced with a malicious version, and Gatekeeper won’t even blink its virtual eye.
Locally built
That also means the attack is not that straightforward to pull off. The threat actor needs to have a way to execute user-level code (for example, a malicious app, a compromised software package installed through a package manager, or a prompt injection attack that tricks an AI agent).
Once that is obtained, they can archive a legitimate app, remove the original, then replace it with malware, and Gatekeeper will not try to re-authorize it. That malicious version can then trick the victim into compromising the device even further, since a certain level of trust was already established.
After reporting the issue to Apple, the company apparently just closed it.
"Apple doesn't consider this attack to be 'modifying' the signed executable," Mysk said. "Instead, Apple says that by archiving/restoring the app bundle, the proof-of-concept code overwrites the entire app bundle, making it locally built. Locally built app bundles are not covered by macOS guards. And this is why access to Keychain or TCC protected directories require system authorization prompts. And for users to accept those is a matter of social engineering attacks that Apple considers out of scope."
Via The Register
