CVE-2021-30765 in macOS
Summary
by MITRE • 09/08/2021
An out-of-bounds write was addressed with improved input validation. This issue is fixed in macOS Big Sur 11.5, Security Update 2021-004 Catalina, Security Update 2021-005 Mojave. An application may be able to execute arbitrary code with kernel privileges.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 05/08/2026
This vulnerability represents a critical out-of-bounds write flaw that was resolved through enhanced input validation mechanisms. The issue affected multiple macOS versions including Big Sur 11.5 and various security updates for Catalina and Mojave operating systems. The root cause of this vulnerability lies in insufficient bounds checking during input processing, which allowed malicious data to overwrite adjacent memory locations beyond the intended buffer boundaries. Such flaws typically arise when developers fail to validate input lengths or fail to properly implement memory allocation checks. The vulnerability is classified under CWE-787 which specifically addresses out-of-bounds write conditions that can lead to arbitrary code execution. From an operational perspective, this vulnerability poses a severe threat to system security as it enables attackers to execute arbitrary code with kernel privileges, effectively bypassing user-level security controls and gaining unrestricted access to system resources.
The exploitation of this vulnerability can result in complete system compromise through techniques such as privilege escalation, code injection, and memory corruption attacks. Attackers can leverage the out-of-bounds write condition to manipulate kernel memory structures, potentially leading to the execution of malicious payloads with the highest system privileges. This type of vulnerability aligns with ATT&CK technique T1068 which covers 'Exploitation for Privilege Escalation' and T1059 which covers 'Command and Scripting Interpreter' as attackers may use the compromised kernel access to execute commands with elevated privileges. The vulnerability's impact extends beyond simple code execution to include potential data exfiltration, system instability, and persistent backdoor installation. Security researchers have documented similar patterns in other kernel-level vulnerabilities where improper input validation leads to memory corruption that can be weaponized for advanced persistent threats.
The remediation approach for this vulnerability focuses on implementing robust input validation controls and strengthening memory management practices within the affected system components. Apple's security updates address the issue by enhancing bounds checking mechanisms and improving input sanitization routines that prevent malicious data from exceeding allocated buffer limits. Organizations should prioritize immediate deployment of the available security patches, particularly the Security Update 2021-004 for Catalina and Security Update 2021-005 for Mojave. System administrators should also implement additional monitoring controls to detect potential exploitation attempts and maintain comprehensive audit logs of system activities. The vulnerability highlights the importance of following secure coding practices and conducting regular security assessments of system components. Organizations should also consider implementing network segmentation and privilege separation measures to limit the potential impact of such vulnerabilities, while ensuring that all system components remain up-to-date with the latest security patches. This vulnerability serves as a reminder of the critical importance of kernel-level security and the need for continuous vulnerability management processes.