CVE-2015-5894 in Mac OS X
Summary
by MITRE
The X.509 certificate-trust implementation in Apple OS X before 10.11 does not recognize that the kSecRevocationRequirePositiveResponse flag implies a revocation-checking requirement, which makes it easier for man-in-the-middle attackers to spoof endpoints by leveraging access to a revoked certificate.
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Analysis
by VulDB Data Team • 11/21/2024
The vulnerability described in CVE-2015-5894 represents a critical flaw in Apple's X.509 certificate trust implementation within macOS versions prior to 10.11. This issue stems from the operating system's failure to properly interpret the kSecRevocationRequirePositiveResponse flag during certificate validation processes. The technical implementation error creates a significant security gap that undermines the fundamental trust model of SSL/TLS communications. When this flag is present, it should mandate that certificate revocation checks return a positive response to validate certificate legitimacy, but the affected macOS versions ignore this requirement entirely. This misinterpretation allows attackers to bypass crucial certificate validation steps that should prevent the acceptance of compromised certificates. The vulnerability specifically impacts the certificate trust chain validation mechanism that operates at the system level, affecting all applications and services that rely on macOS's built-in certificate validation routines. The flaw exists in the core security infrastructure that governs how operating systems handle certificate trust decisions, making it particularly dangerous as it affects the fundamental security guarantees of encrypted communications.
The operational impact of this vulnerability is severe and directly enables man-in-the-middle attacks that would otherwise be prevented by proper certificate revocation checking. Attackers can exploit this weakness by obtaining access to revoked certificates and using them to impersonate legitimate endpoints in secure communications. The vulnerability essentially creates a backdoor in the certificate validation process where revoked certificates can be accepted without proper verification of their revocation status. This allows attackers to establish fraudulent secure connections that appear legitimate to end users and applications, as the system fails to perform the necessary revocation checks that would normally detect compromised certificates. The attack vector is particularly insidious because it leverages existing trust relationships within the operating system rather than requiring additional exploitation techniques. This vulnerability affects the entire certificate trust model of macOS, potentially compromising thousands of applications and services that depend on the system's certificate validation capabilities for secure communications. The flaw enables attackers to bypass security controls designed to detect and prevent the use of compromised certificates, creating a persistent threat that can be exploited across multiple applications and network protocols.
The technical nature of this vulnerability aligns with CWE-295 which addresses improper certificate validation, and it directly relates to ATT&CK technique T1552.001 for credentials from password storage. The implementation flaw represents a failure in certificate validation logic that should have been caught during security testing of the operating system's cryptographic components. The kSecRevocationRequirePositiveResponse flag is part of Apple's Security framework API and should have triggered mandatory revocation checking behavior. This vulnerability demonstrates a critical oversight in the security architecture where the system's trust model fails to enforce proper certificate lifecycle management. The impact extends beyond simple certificate validation to affect the integrity of all secure communications relying on X.509 certificates within the affected operating system versions. Security researchers identified that this issue was particularly dangerous because it affected the operating system's core security functions rather than individual applications, making it a systemic vulnerability that required immediate attention and patching across all affected installations.
Organizations and users should immediately upgrade to macOS 10.11 or later versions to remediate this vulnerability, as the patch addresses the core implementation flaw in the certificate validation logic. System administrators should conduct thorough vulnerability assessments to identify any applications or services that might be affected by this certificate trust issue, particularly those relying on macOS's built-in certificate validation. The mitigation strategy should include monitoring for any attempts to use revoked certificates in secure communications and implementing additional network-level detection measures. Security teams should also review their certificate management practices to ensure proper revocation checking is implemented at the application level, even when the operating system's certificate validation is compromised. Organizations using custom certificate validation logic or third-party security tools should verify that their implementations properly handle the kSecRevocationRequirePositiveResponse flag and maintain independent verification of certificate status. The vulnerability underscores the importance of proper certificate lifecycle management and the need for robust revocation checking mechanisms in all security infrastructure components. Regular security audits should include assessment of certificate trust model implementations to prevent similar issues in other cryptographic systems and ensure comprehensive protection against man-in-the-middle attacks and certificate-based impersonation attempts.