CVE-2016-4644 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 downgrade issue existed with HTTP authentication credentials saved in Keychain. This issue was addressed by storing the authentication types with the credentials.
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Analysis
by VulDB Data Team • 04/28/2020
The vulnerability described in CVE-2016-4644 represents a significant security flaw in Apple's operating systems that affected iOS versions prior to 9.3.3, tvOS prior to 9.2.2, and OS X El Capitan before v10.11.6 and Security Update 2016-004. This issue specifically targeted the handling of HTTP authentication credentials stored within the system keychain, creating a potential vector for credential compromise and unauthorized access to protected resources. The flaw was categorized under the Common Weakness Enumeration framework as a weakness related to improper handling of authentication credentials, specifically falling within CWE-522 which addresses insufficiently Protected Credentials. The vulnerability exploited a downgrade scenario where authentication types were not properly stored alongside credentials, allowing attackers to manipulate the authentication process and potentially gain access to systems or services that required specific authentication methods.
The technical implementation of this vulnerability stemmed from how Apple's keychain services managed stored authentication credentials across different operating system versions. When users saved HTTP authentication credentials for websites or network services, the system failed to maintain the specific authentication type information alongside the credential data. This meant that during authentication processes, the system could potentially downgrade to less secure authentication methods or incorrectly interpret the stored credentials, particularly when users accessed services that required specific authentication mechanisms such as basic authentication versus digest authentication. The issue created a scenario where previously stored credentials could be misused or interpreted incorrectly, potentially allowing attackers to bypass intended security controls or access resources with reduced authentication security.
The operational impact of CVE-2016-4644 extended beyond simple credential theft, as it could enable attackers to perform unauthorized access to network services, web applications, and enterprise resources that relied on HTTP authentication. This vulnerability particularly affected environments where users frequently accessed multiple services with varying authentication requirements, as the system's inability to properly maintain authentication type information could lead to automatic downgrading to weaker authentication methods. Security researchers noted that this flaw could be exploited in conjunction with other attack vectors, potentially allowing for more sophisticated credential manipulation attacks. The vulnerability's impact was particularly concerning for enterprise environments where users might have stored credentials for various internal services, as the downgrade capability could provide attackers with access to sensitive corporate resources.
Apple addressed this vulnerability by implementing enhanced credential storage mechanisms that ensured authentication types were properly maintained alongside stored credentials within the keychain system. This fix aligned with recommended practices for secure credential management and addressed the specific weakness identified in the authentication handling process. The security update required that when credentials were saved, the system would explicitly store and associate the authentication type with each credential entry, preventing the automatic downgrade scenario that previously existed. Organizations implementing mitigations should have updated their systems to the patched versions, ensuring that all affected devices received the necessary security updates. The resolution also reinforced industry best practices for credential management as outlined in various security frameworks and standards, including the NIST Cybersecurity Framework and ISO/IEC 27001 requirements for secure authentication and access control. This vulnerability highlighted the importance of proper credential lifecycle management and the need for robust authentication type preservation in secure system design.