CVE-2016-4740 in iOS
Summary
by MITRE
Apple iOS before 10, when Handoff for Messages is used, does not ensure that a Messages signin has occurred before displaying messages, which might allow attackers to obtain sensitive information via unspecified vectors.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 09/16/2022
The vulnerability described in CVE-2016-4740 represents a significant security flaw in Apple iOS versions prior to 10.0 that affects the Handoff functionality for Messages. This issue stems from improper authentication verification mechanisms within the Handoff protocol implementation, specifically when users transition between devices while using Messages. The flaw creates a window of opportunity where unauthorized parties can potentially access sensitive messaging data without proper authentication, exploiting the lack of strict signin verification before displaying message content.
The technical implementation of this vulnerability occurs within the Handoff feature's message synchronization process. When Handoff is enabled for Messages, iOS devices attempt to seamlessly transfer messaging sessions between connected devices. However, the system fails to enforce mandatory authentication checks before displaying message content on the receiving device, creating a race condition where messages appear before proper verification occurs. This design flaw allows attackers to intercept and display messages from other users' accounts on devices that support Handoff functionality. The vulnerability manifests through unspecified vectors that likely involve network interception, device proximity attacks, or manipulation of the Handoff handshake process, potentially enabling information disclosure attacks against iOS users.
The operational impact of CVE-2016-4740 extends beyond simple privacy concerns to encompass potential data breaches and unauthorized access to sensitive communications. Attackers could exploit this vulnerability to access personal conversations, financial information, or other confidential data transmitted through iMessage when users have Handoff enabled. The vulnerability affects all iOS versions before 10.0, representing a substantial attack surface that could be leveraged by threat actors in various scenarios including public Wi-Fi network attacks, device proximity exploitation, or man-in-the-middle interception attempts. This flaw particularly impacts users who frequently use Handoff between their iPhone, iPad, and Mac devices, as the vulnerability can be triggered through legitimate Handoff operations.
This vulnerability aligns with CWE-284, which addresses improper access control, and demonstrates weaknesses in authentication and session management within Apple's Handoff implementation. The attack pattern follows ATT&CK technique T1566 for credential access through social engineering or network attacks, while also relating to T1071 for application layer protocol usage in message interception. Organizations and users should immediately update to iOS 10.0 or later to remediate this vulnerability, as the patch addresses the authentication flow and ensures proper message signin verification before content display. Additional mitigations include disabling Handoff for Messages in device settings when not actively needed, implementing network monitoring to detect unusual Handoff activity, and maintaining awareness of potential social engineering attacks that could exploit this weakness in conjunction with other vulnerabilities. The vulnerability underscores the importance of proper authentication enforcement in cross-device synchronization protocols and highlights the risks associated with seamless connectivity features that may compromise security boundaries.