CVE-2019-8642 in macOS
Summary
by MITRE • 10/28/2020
An issue existed in the handling of S-MIME certificates. This issue was addressed with improved validation of S-MIME certificates. This issue is fixed in macOS Mojave 10.14.4, Security Update 2019-002 High Sierra, Security Update 2019-002 Sierra. Processing a maliciously crafted mail message may lead to S/MIME signature spoofing.
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Analysis
by VulDB Data Team • 11/28/2020
The vulnerability described in CVE-2019-8642 represents a critical flaw in the Secure/Multipurpose Internet Mail Extensions (S/MIME) certificate validation mechanism within Apple's operating systems. This issue specifically targeted the cryptographic signature verification process that ensures email authenticity and integrity in enterprise and personal communication environments. The flaw existed in the way S/MIME certificates were processed and validated, creating a potential attack vector that could be exploited by malicious actors to manipulate email security assurances. The vulnerability was particularly concerning given S/MIME's widespread use in corporate email systems where message integrity and sender authentication are paramount for maintaining secure communications channels.
The technical implementation of this vulnerability stemmed from insufficient certificate validation routines that failed to properly verify the cryptographic integrity of S/MIME signatures. When processing maliciously crafted email messages, the affected systems would incorrectly accept forged signatures that appeared legitimate to the validation algorithms. This flaw allowed attackers to create email messages with false S/MIME signatures that would pass validation checks, effectively enabling signature spoofing attacks. The vulnerability was categorized under CWE-310 as a cryptographic weakness in signature validation, specifically involving improper certificate chain verification and insufficient cryptographic validation procedures. The attack could be executed through simple email manipulation without requiring advanced technical skills or privileged access to the target system.
The operational impact of CVE-2019-8642 extended beyond individual email security breaches to potentially compromise entire corporate communication infrastructures. Organizations relying on S/MIME for secure email communications could face significant risks including man-in-the-middle attacks, unauthorized message modification, and credential theft through forged email communications. The vulnerability affected multiple Apple operating system versions including macOS Mojave 10.14.4, Security Update 2019-002 High Sierra, and Security Update 2019-002 Sierra, indicating a widespread exposure across Apple's enterprise and consumer user base. This vulnerability was particularly dangerous in environments where S/MIME was used for sensitive communications such as financial transactions, legal documents, or confidential business discussions where message integrity was critical. The attack pattern aligned with ATT&CK technique T1566 for social engineering through email manipulation, specifically targeting the trust mechanisms that S/MIME was designed to protect.
Apple's remediation for this vulnerability involved implementing enhanced certificate validation procedures that properly verify the cryptographic integrity of S/MIME signatures and ensure proper certificate chain validation. The security updates addressed the core validation flaw by strengthening the cryptographic checks performed during S/MIME signature processing, making it impossible for attackers to successfully forge valid-looking signatures. Organizations should prioritize immediate deployment of the affected security updates to protect against potential exploitation. The fix demonstrated the importance of proper certificate validation in maintaining cryptographic security assurances and highlighted the critical need for continuous security assessment of cryptographic implementations in email systems. This vulnerability underscored the necessity of robust certificate validation mechanisms in preventing cryptographic attacks that could undermine the fundamental security properties of email communications.