CVE-2009-0161 in Mac OS X
Summary
by MITRE
The OpenSSL::OCSP module for Ruby in Apple Mac OS X 10.5 before 10.5.7 misinterprets an unspecified invalid response as a successful OCSP certificate validation, which might allow remote attackers to spoof certificate authentication via a revoked certificate.
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Analysis
by VulDB Data Team • 05/27/2025
The vulnerability described in CVE-2009-0161 represents a critical flaw in the OpenSSL::OCSP module implementation within Apple Mac OS X 10.5 operating system versions prior to 10.5.7. This issue stems from improper handling of OCSP (Online Certificate Status Protocol) responses where the system fails to correctly interpret certain invalid or malformed responses. The vulnerability specifically affects the certificate validation process that occurs when a system attempts to verify the status of digital certificates through OCSP requests. When an OCSP responder returns an invalid response, the affected Mac OS X versions incorrectly treat this as a successful validation, effectively bypassing the intended security checks that should prevent the use of revoked certificates.
The technical nature of this vulnerability lies in the improper state management and response parsing logic within the OpenSSL::OCSP module. According to CWE-252, this represents an issue where the system fails to check for an error condition that should result in a failure state. The flaw occurs during the certificate validation process where the system should reject malformed or invalid OCSP responses but instead accepts them as valid. This misinterpretation creates a scenario where attackers can exploit the vulnerability by crafting malicious OCSP responses that appear legitimate to the vulnerable system, thereby allowing them to present revoked certificates as if they were valid. The vulnerability essentially creates a trust boundary failure where the certificate validation mechanism becomes compromised, enabling unauthorized certificate authentication.
The operational impact of this vulnerability is significant as it undermines the fundamental security model of certificate-based authentication systems. Attackers can exploit this weakness to perform man-in-the-middle attacks, bypass certificate revocation checks, and potentially gain unauthorized access to systems that rely on certificate validation for authentication. The vulnerability affects any application or service that depends on the OpenSSL::OCSP module for certificate validation, including web browsers, email clients, and network services that use SSL/TLS certificates. According to ATT&CK framework, this vulnerability maps to T1556.004 - Credentials from Password Stores, as it enables attackers to bypass certificate validation mechanisms and gain access to systems that should be protected by proper certificate status checking. The flaw particularly affects environments where certificate revocation is critical for maintaining security posture, such as enterprise networks, web applications, and secure communication channels.
Mitigation strategies for this vulnerability involve applying the official security patches released by Apple for Mac OS X 10.5.7 and later versions. Organizations should prioritize updating their systems to ensure that the patched OpenSSL::OCSP module correctly handles invalid responses and properly rejects malformed OCSP replies. Additionally, system administrators should consider implementing additional certificate validation checks and monitoring mechanisms to detect potential exploitation attempts. The vulnerability highlights the importance of proper error handling in cryptographic libraries and demonstrates the critical need for robust validation of external responses in security-sensitive applications. Organizations should also review their certificate management policies and consider implementing certificate pinning techniques to provide additional layers of protection against such certificate validation bypasses. Security teams should monitor for any signs of exploitation attempts and maintain awareness of the specific attack vectors that leverage this vulnerability to maintain comprehensive security posture.