CVE-2016-4643 in macOS
Summary
by MITRE
In iOS before 9.3.3, tvOS before 9.2.2, and OS X El Capitan before v10.11.6 and Security Update 2016-004, a validation issue existed in the parsing of 407 responses. This issue was addressed through improved response validation.
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Analysis
by VulDB Data Team • 04/28/2020
The vulnerability described in CVE-2016-4643 represents a critical validation flaw in Apple's handling of HTTP 407 proxy authentication responses across multiple operating systems. This issue affected iOS versions prior to 9.3.3, tvOS versions prior to 9.2.2, and OS X El Capitan versions prior to v10.11.6, along with Security Update 2016-004. The flaw specifically targeted the parsing mechanism for HTTP 407 responses which are used by web proxies to request authentication credentials from clients. This vulnerability falls under CWE-20, which describes improper input validation, and represents a classic example of how inadequate response handling can create security risks in network protocols. The issue stems from the improper validation of proxy authentication responses, allowing for potential manipulation of authentication flows that could be exploited by malicious actors.
The technical implementation of this vulnerability occurs when the affected Apple operating systems receive HTTP 407 responses from proxy servers. The system's parsing logic fails to properly validate the structure and content of these responses, creating opportunities for attackers to craft malicious responses that could bypass authentication mechanisms or manipulate the proxy authentication process. This validation failure enables attackers to potentially inject malformed data or manipulate the authentication flow, leading to unauthorized access or disruption of proxy-based network services. The vulnerability specifically impacts the way these systems process the authentication challenges returned by proxy servers, potentially allowing for credential theft or unauthorized network access. From an attack perspective, this issue aligns with ATT&CK technique T1071.004 for application layer protocol: DNS and T1566.001 for credential access through proxy authentication manipulation.
The operational impact of CVE-2016-4643 extends beyond simple authentication bypass scenarios, as it could enable attackers to establish persistent access through compromised proxy authentication flows. Organizations relying on proxy-based network architectures would face significant risks, as this vulnerability could allow unauthorized users to gain access to network resources that should be protected by proxy authentication. The vulnerability's presence in multiple Apple platforms including mobile devices, television systems, and desktop operating systems creates a broad attack surface. Network administrators and security professionals would need to implement immediate mitigations, as the flaw could be exploited in man-in-the-middle attacks or credential harvesting scenarios. The vulnerability particularly impacts environments where proxy authentication is required for network access, making it a significant concern for enterprise security. The security update released by Apple addressed this through improved validation mechanisms that ensure proper parsing of HTTP 407 responses and prevent malformed data from being processed during the authentication handshake.
Mitigation strategies for CVE-2016-4643 require immediate deployment of Apple's security updates across all affected platforms, including iOS devices, tvOS systems, and OS X El Capitan installations. Organizations should also implement network monitoring to detect anomalous proxy authentication behavior and consider implementing additional authentication layers beyond proxy-based systems. Security teams should review proxy server configurations and ensure that proper certificate validation is in place to prevent man-in-the-middle attacks that could exploit this vulnerability. The remediation process must include thorough testing of proxy authentication flows to ensure that the updated validation mechanisms function correctly without disrupting legitimate network operations. Additionally, security awareness training should be conducted to ensure that users understand the importance of keeping their systems updated and the potential risks associated with unpatched authentication mechanisms. This vulnerability demonstrates the critical importance of proper input validation in network protocol implementations and serves as a reminder of the security implications of authentication flow handling in enterprise environments.