CVE-2021-1840 in macOS
Summary
by MITRE • 09/08/2021
A memory corruption issue was addressed with improved validation. This issue is fixed in macOS Big Sur 11.3, Security Update 2021-002 Catalina, Security Update 2021-003 Mojave. A local attacker may be able to elevate their privileges.
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Analysis
by VulDB Data Team • 06/15/2026
This memory corruption vulnerability represents a critical security flaw that could enable local attackers to escalate their privileges within affected systems. The issue stems from inadequate input validation mechanisms that fail to properly sanitize or verify memory operations, creating potential entry points for malicious actors to manipulate system processes. The vulnerability affects multiple versions of apple's operating systems including macOS big sur 11.3 and various security updates for catalina and mojave releases, indicating a widespread impact across the apple ecosystem. The root cause aligns with common software security weaknesses categorized under cwe-121 heap-based buffer overflow or cwe-122 stack-based buffer overflow patterns, where insufficient bounds checking allows attackers to overwrite adjacent memory locations. When exploited, this vulnerability could enable an attacker with local access to potentially gain elevated privileges, effectively bypassing standard user permissions and system security controls. The privilege escalation occurs through memory corruption techniques that manipulate kernel or system memory structures, allowing malicious code execution with higher privileges than initially granted. This type of vulnerability falls under the attack pattern category of privilege escalation as defined in the attack technique framework, specifically targeting the execution of code with elevated system privileges. The security implications extend beyond simple local exploitation since successful privilege escalation could provide attackers with complete system control, potentially enabling data exfiltration, persistent access, or further network infiltration. The fix implemented in the security updates addresses the validation gaps by strengthening input sanitization processes and implementing more robust memory management controls. These patches typically involve enhanced bounds checking mechanisms, improved memory allocation procedures, and additional validation steps that prevent malicious data from corrupting critical system memory regions. The vulnerability demonstrates the importance of comprehensive memory safety practices in system software development, particularly in operating system kernels where memory corruption can lead to complete system compromise. Organizations should prioritize deployment of these security updates immediately, as the window for exploitation remains open until systems are properly patched. The issue highlights the ongoing challenge of memory safety in complex software systems and underscores the necessity of regular security maintenance and patch management processes to protect against known vulnerabilities. Legacy system support considerations must also be addressed since older versions like mojave continue to receive security updates, but may have limited compatibility with newer patching mechanisms. The vulnerability serves as a reminder of the critical importance of secure coding practices and memory management validation in preventing privilege escalation attacks that could compromise entire computing environments.