CVE-2021-30876 in macOS
Summary
by MITRE • 08/25/2021
An out-of-bounds read was addressed with improved bounds checking. This issue is fixed in macOS Monterey 12.0.1, Security Update 2021-007 Catalina, macOS Big Sur 11.6.1. Processing a maliciously crafted AppleScript binary may result in unexpected application termination or disclosure of process memory.
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Analysis
by VulDB Data Team • 10/31/2021
The vulnerability identified as CVE-2021-30876 represents a critical out-of-bounds read flaw within Apple's macOS operating system that was addressed through enhanced bounds checking mechanisms. This issue specifically affects the processing of AppleScript binary files and demonstrates the inherent risks associated with improper memory validation in system-level components. The vulnerability stems from insufficient input validation when handling crafted AppleScript binary content, creating opportunities for attackers to exploit memory access patterns that exceed allocated boundaries.
The technical implementation of this flaw involves the AppleScript interpreter's failure to properly validate array indices or buffer limits when processing maliciously crafted binary AppleScript files. This type of vulnerability falls under the CWE-129 category of Improper Validation of Array Index, which directly relates to the unchecked memory access patterns that lead to out-of-bounds reads. The vulnerability operates at the kernel level within the macOS system architecture, specifically within the AppleScript processing subsystem that handles binary script execution. When an application processes a malicious AppleScript binary, the interpreter attempts to access memory locations beyond the intended boundaries, potentially causing application crashes or exposing sensitive process memory contents.
The operational impact of CVE-2021-30876 extends beyond simple application instability to encompass potential information disclosure and system compromise scenarios. An attacker who successfully exploits this vulnerability could achieve unexpected application termination, which might be leveraged as a denial-of-service vector, or more critically, gain access to process memory contents that could reveal sensitive data such as cryptographic keys, user credentials, or system configuration information. This vulnerability aligns with ATT&CK technique T1059.007 for AppleScript execution and represents a classic example of how scripting language vulnerabilities can be weaponized to bypass system security controls. The memory disclosure aspect particularly concerns security practitioners as it could enable further exploitation attempts or information gathering activities that compromise system integrity.
The remediation for this vulnerability required Apple to implement comprehensive bounds checking mechanisms within the AppleScript processing framework, ensuring that all array access operations and memory allocations are properly validated before execution. The affected versions include macOS Big Sur 11.6.1, macOS Catalina with Security Update 2021-007, and the initial release of macOS Monterey 12.0.1, demonstrating Apple's commitment to addressing memory safety issues in their operating system. Security professionals should note that this vulnerability highlights the importance of proper input validation in system-level components and the potential consequences of insufficient bounds checking in interpreted scripting environments. The fix implemented by Apple represents a standard approach to mitigating out-of-bounds read vulnerabilities through enhanced memory validation and bounds checking procedures. Organizations should prioritize deployment of these security updates to protect against potential exploitation attempts targeting AppleScript processing capabilities within their macOS environments.