CVE-2016-4605 in iOS
Summary
by MITRE
Calendar in Apple iOS before 9.3.3 allows remote attackers to cause a denial of service (NULL pointer dereference and device restart) via a crafted invitation.
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Analysis
by VulDB Data Team • 09/05/2022
The vulnerability identified as CVE-2016-4605 represents a critical denial of service flaw within Apple iOS calendar functionality affecting versions prior to 9.3.3. This vulnerability stems from improper input validation in the calendar invitation processing mechanism, where maliciously crafted calendar invitations can trigger unexpected system behavior. The flaw manifests as a NULL pointer dereference condition that occurs when the iOS calendar application attempts to process malformed invitation data, leading to abrupt system termination and device restart. The vulnerability is particularly concerning because it can be exploited remotely through calendar invitations sent via email, iMessage, or other calendar synchronization protocols, requiring no physical access to the target device and allowing attackers to disrupt calendar services without authentication.
The technical implementation of this vulnerability involves the calendar application's failure to properly validate invitation data structures before attempting to dereference pointers within the invitation processing pipeline. When a maliciously crafted invitation contains malformed or unexpected data fields, the calendar component attempts to access memory locations that have not been properly initialized, resulting in a NULL pointer dereference. This memory access violation causes the calendar application to crash and restart, effectively creating a denial of service condition that prevents legitimate calendar operations. The vulnerability maps to CWE-476 which specifically addresses NULL pointer dereference conditions in software implementations, and aligns with ATT&CK technique T1499.002 which covers network denial of service attacks targeting system services.
The operational impact of CVE-2016-4605 extends beyond simple service disruption as it can be leveraged in various attack scenarios including targeted attacks against specific individuals or organizations. The remote exploitation capability means that attackers can deploy this vulnerability through email campaigns or calendar sharing protocols without requiring any special privileges or physical access to affected devices. Organizations relying on iOS devices for business operations may experience significant disruption when employees receive malicious calendar invitations, potentially affecting productivity and communication workflows. The automatic nature of calendar invitation processing means that victims may not even realize they have been targeted until their device experiences unexpected restarts, making this vulnerability particularly stealthy and dangerous in enterprise environments where calendar synchronization is critical for business operations.
Mitigation strategies for CVE-2016-4605 primarily focus on immediate system updates and administrative controls. The most effective remediation involves upgrading affected iOS devices to version 9.3.3 or later, which includes patches addressing the NULL pointer dereference condition in calendar processing. System administrators should implement comprehensive mobile device management policies to ensure timely deployment of security updates across all enterprise devices. Additional defensive measures include implementing calendar filtering rules to block invitations from untrusted sources, enabling calendar application sandboxing where possible, and monitoring for unusual calendar activity patterns that may indicate exploitation attempts. Network-level protections such as email filtering and calendar synchronization protocol restrictions can provide additional layers of defense, while user education about recognizing suspicious calendar invitations helps reduce successful exploitation attempts. The vulnerability highlights the importance of proper input validation in mobile application development and demonstrates how seemingly minor flaws in calendar processing can result in significant system availability issues.