CVE-2018-4398 in macOS
Summary
by MITRE
An issue existed in the method for determining prime numbers. This issue was addressed by using pseudorandom bases for testing of primes. This issue affected versions prior to iOS 12.1, macOS Mojave 10.14.1, tvOS 12.1, watchOS 5.1, iTunes 12.9.1, iCloud for Windows 7.8.
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Analysis
by VulDB Data Team • 06/03/2023
The vulnerability described in CVE-2018-4398 represents a critical weakness in cryptographic prime number generation mechanisms that underpin secure communications and encryption systems. This flaw existed in Apple's implementation of prime number testing algorithms across multiple operating systems and applications, creating potential pathways for attackers to compromise the security of cryptographic operations. The issue stems from the use of deterministic or predictable methods for prime verification, which can be exploited by adversaries to weaken the cryptographic foundation of affected systems. The vulnerability specifically impacted versions of iOS, macOS, tvOS, watchOS, and related applications before their respective security updates, leaving millions of devices exposed to potential cryptographic attacks. This type of weakness directly violates fundamental security principles that require cryptographically secure random number generation for critical operations.
The technical flaw in CVE-2018-4398 manifests as insufficient randomness in the prime number testing process, particularly in the selection of bases used for primality testing algorithms. Traditional prime testing methods such as the Miller-Rabin test require pseudorandom bases to ensure cryptographic security, but the vulnerable implementations used predictable or insufficiently random values. This weakness falls under the category of weak randomness in cryptographic implementations, which is classified as CWE-330, and represents a direct violation of the NIST SP 800-90A standard for random number generation. The predictable nature of the prime testing bases means that attackers could potentially reverse-engineer or predict the testing process, undermining the security of RSA key generation and other cryptographic operations that depend on large prime numbers. This vulnerability specifically affects the mathematical foundations of public key cryptography, where the security relies on the difficulty of factoring large composite numbers, making it a critical concern for system security.
The operational impact of CVE-2018-4398 extends far beyond simple cryptographic weakness, as it could enable attackers to perform sophisticated attacks against encrypted communications, digital signatures, and authentication mechanisms. Systems affected by this vulnerability could be compromised through attacks that exploit the predictable prime testing process to weaken cryptographic keys or bypass security controls. The exposure affected widely used platforms including mobile devices, desktop operating systems, and cloud synchronization services, creating extensive attack surface for potential exploitation. This vulnerability could facilitate man-in-the-middle attacks, certificate forgery, and unauthorized access to encrypted data, as the weakened prime generation process undermines the security assumptions of cryptographic protocols. The impact is particularly severe given that the vulnerability affected multiple Apple platforms and applications, including iTunes and iCloud for Windows, creating potential cross-platform attack vectors that could compromise user data across different device types and operating environments.
Apple's resolution of CVE-2018-4398 involved implementing proper pseudorandom base selection for prime number testing, ensuring that cryptographic operations use cryptographically secure random number generators as recommended by industry standards. The fix addressed the root cause by updating the prime testing algorithms to use sufficient entropy in base selection, thereby restoring the mathematical security guarantees required for cryptographic operations. Organizations should ensure that all affected systems are updated to the patched versions, as the vulnerability could be exploited by attackers with sufficient resources to perform mathematical attacks on weakened cryptographic implementations. Security teams should monitor for any indicators of exploitation attempts and verify that systems have been properly updated to prevent potential compromise of encrypted communications and authentication systems. The remediation process should include verification that all affected applications and operating system versions have been updated, as the vulnerability could persist in older versions that have not received the necessary security patches. This vulnerability highlights the importance of proper cryptographic implementation practices and the necessity of following established security standards such as those defined in the NIST Cryptographic Standards and the OWASP Cryptographic Implementation Guidelines.