CVE-2011-3427 in Mac OS X
Summary
by MITRE
The Data Security component in Apple iOS before 5 and Apple TV before 4.4 does not properly restrict use of the MD5 hash algorithm within X.509 certificates, which makes it easier for man-in-the-middle attackers to spoof servers or obtain sensitive information via a crafted certificate.
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Analysis
by VulDB Data Team • 06/01/2021
The vulnerability identified as CVE-2011-3427 represents a significant cryptographic weakness in Apple's implementation of X.509 certificate validation across iOS versions prior to 5.0 and Apple TV versions prior to 4.4. This flaw resides within the Data Security component that governs how certificates are processed and validated during secure communications. The issue stems from insufficient restrictions on the use of the MD5 hash algorithm, which has been widely deprecated due to its known cryptographic vulnerabilities and susceptibility to collision attacks. The weakness creates a pathway for adversaries to exploit the certificate validation process and compromise the integrity of secure communications.
The technical implementation flaw occurs when the system fails to properly enforce restrictions on MD5 hash usage within X.509 certificates, allowing certificates that employ this weak hashing algorithm to be accepted as valid. This vulnerability directly relates to CWE-327, which addresses the use of weak cryptographic algorithms, and specifically targets the improper restriction of cryptographic algorithms within certificate validation mechanisms. The MD5 algorithm's collision resistance has been thoroughly compromised since 2005, making it trivial for attackers to generate certificates that appear legitimate while actually containing malicious content or enabling impersonation of trusted entities.
From an operational perspective, this vulnerability enables man-in-the-middle attackers to conduct sophisticated spoofing attacks against secure communications. Attackers can generate forged certificates that exploit the MD5 weakness to bypass certificate validation checks, allowing them to intercept and manipulate encrypted traffic between clients and servers. The impact extends beyond simple eavesdropping to include potential credential theft, session hijacking, and data exfiltration from compromised systems. This weakness particularly affects web browsing, email communications, and any application relying on SSL/TLS certificates for authentication and encryption, making it a critical threat to enterprise and personal security.
The mitigation strategy involves updating affected Apple devices to the patched versions that properly enforce restrictions on MD5 hash usage within certificate validation. System administrators should ensure all iOS and Apple TV devices are upgraded to versions that disable MD5-based certificate validation and enforce stronger hashing algorithms such as SHA-256 or higher. Organizations should also implement certificate pinning mechanisms where possible and monitor for any continued use of MD5-based certificates in their networks. The remediation aligns with ATT&CK technique T1552.001, which covers the exploitation of weak cryptographic implementations, and represents a fundamental requirement for maintaining secure communications in accordance with NIST SP 800-57 cryptographic standards.