CVE-2021-1877 in iOS
Summary
by MITRE • 09/08/2021
An out-of-bounds read was addressed with improved input validation. This issue is fixed in iOS 14.5 and iPadOS 14.5. A local user may be able to read kernel memory.
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Analysis
by VulDB Data Team • 06/23/2026
This vulnerability represents a critical out-of-bounds read flaw that existed within the kernel-level memory management systems of ios and ipad os versions prior to 14.5. The issue stems from insufficient input validation mechanisms that fail to properly sanitize or verify data boundaries before processing memory access requests. When malicious code or applications attempt to access memory locations beyond their allocated bounds, the system's inadequate validation allows unauthorized reading of kernel memory regions that should remain protected from user-space processes.
The technical nature of this vulnerability aligns with common software security weaknesses categorized under cwe-129 and cwe-787, which specifically address issues related to improper input validation and out-of-bounds read conditions. Attackers exploiting this flaw could potentially extract sensitive kernel data including system credentials, memory addresses, or other confidential information that would normally be restricted from access by regular applications or local users. This represents a significant escalation of privileges since it allows local users to bypass normal security boundaries that typically separate user-space applications from the core operating system components.
The operational impact of this vulnerability extends beyond simple data exposure, as it creates potential pathways for more sophisticated attacks including privilege escalation and system compromise. While the vulnerability requires local access to exploit, it provides attackers with the capability to read kernel memory directly, which could reveal information useful for developing further exploits or conducting advanced persistent threats. The fix implemented in ios 14.5 and ipad os 14.5 addresses this by strengthening input validation routines that check memory access boundaries before allowing any kernel-level operations to proceed.
Organizations should prioritize updating affected systems to ios 14.5 or later versions as soon as possible, since this vulnerability could be leveraged in combination with other exploits to achieve complete system compromise. The mitigation strategy involves not only applying the official patches but also implementing network monitoring to detect potential exploitation attempts that might occur during the transition period. Security teams should monitor for anomalous memory access patterns or unusual kernel behavior that might indicate attempted exploitation of this vulnerability. Additionally, organizations should consider implementing additional layers of protection including kernel hardening techniques and runtime application control measures to further reduce the attack surface.
From an att&ck framework perspective, this vulnerability maps to techniques involving privilege escalation and credential access through kernel-level exploits. The remediation process should include comprehensive testing of patched systems to ensure that the input validation improvements function correctly without introducing regressions in system functionality. System administrators should also review existing security policies and consider implementing more robust monitoring for kernel memory access patterns as part of their ongoing security operations. The vulnerability demonstrates the critical importance of maintaining up-to-date operating system versions and proper security patch management procedures across all organizational endpoints.