Apple macOS Gatekeeper Security Bypass and Malware Execution Vulnerability (CVE-2021-30657)

1. Vulnerability Overview & Root Cause

This vulnerability (CVE-2021-30657) stems from a logic issue in the state management of macOS's Gatekeeper security framework. Normally, macOS assigns a quarantine flag (com.apple.quarantine) to files downloaded from the internet and subjects them to Gatekeeper and Notarization checks. However, a logic flaw existed where certain malformed application bundle structures (such as those missing the 'Info.plist' file) failed to trigger the quarantine verification process, allowing the execution engine to bypass security checks entirely.

2. Exploitation Mechanics & Attack Scenario

In active exploitation scenarios (such as those involving the Shlayer malware family), attackers crafted a double-clickable application bundle (.app) but intentionally omitted the standard 'Info.plist' metadata file. When a user executes this crafted bundle, the macOS LaunchServices and kernel treat it as a basic script or raw executable rather than a standard app bundle. Consequently, Gatekeeper fails to perform quarantine and notarization checks, executing the untrusted payload immediately without displaying any security warnings to the user.

3. Infrastructure & Business Impact

As this vulnerability is listed in the CISA KEV catalog, it represents a highly practical and actively exploited threat vector. In an enterprise environment, successful exploitation allows attackers to bypass endpoint protection controls, establish initial access, deploy secondary payloads, and potentially move laterally across the corporate network, posing a severe risk of data exfiltration and ransomware deployment.