CVE-2017-13871 in macOS
Summary
by MITRE
An issue was discovered in certain Apple products. macOS before 10.13.2 is affected. The issue involves the "Mail" component. It allows remote attackers to read cleartext e-mail content (for which S/MIME encryption was intended) by leveraging the lack of installation of an S/MIME certificate by the recipient.
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Analysis
by VulDB Data Team • 08/18/2024
The vulnerability identified as CVE-2017-13871 represents a significant security flaw in Apple's macOS Mail application affecting versions prior to 10.13.2. This issue specifically targets the S/MIME encryption implementation within the email client, creating a critical gap in end-to-end email security that adversaries can exploit to compromise sensitive communications. The vulnerability stems from a fundamental misconfiguration in how the Mail application handles S/MIME encrypted messages when the recipient's certificate is not properly installed or configured on their device.
The technical flaw manifests when users attempt to read S/MIME encrypted emails without having the corresponding certificate installed in their keychain. This creates a scenario where the Mail application fails to properly validate the encryption status of incoming messages, allowing attackers to intercept and read the cleartext content that was originally intended to be protected through S/MIME encryption. The vulnerability operates at the application layer and specifically affects the cryptographic validation mechanisms that should ensure only authorized recipients can decrypt sensitive email content. This represents a violation of the confidentiality principle in the CIA triad, where the intended encryption protection is bypassed due to improper certificate handling within the email client's security framework.
The operational impact of this vulnerability extends beyond simple information disclosure, as it undermines the trust model that organizations rely upon when implementing S/MIME encryption for secure communications. Attackers can leverage this weakness to perform man-in-the-middle attacks on email communications, particularly targeting business-critical messages that contain sensitive financial, legal, or personal information. The vulnerability is particularly concerning in enterprise environments where S/MIME is commonly deployed to protect confidential communications between organizations, as it effectively nullifies the encryption protections that security policies assume are in place. This weakness can be exploited remotely without requiring any special privileges or access to the target system, making it an attractive vector for threat actors seeking to compromise email confidentiality.
From a cybersecurity perspective, this vulnerability aligns with CWE-310, which addresses cryptographic issues and improper certificate validation. The flaw demonstrates a failure in certificate management and validation processes that should ensure proper cryptographic security measures are maintained. Organizations implementing email security policies based on S/MIME encryption may find their security posture significantly weakened if users are not properly managing their certificate installations. The vulnerability also relates to ATT&CK technique T1566, which covers social engineering attacks, as it could be exploited through phishing campaigns that target users to deliver malicious emails that bypass encryption protections.
Mitigation strategies for CVE-2017-13871 require immediate system updates to macOS 10.13.2 or later versions where Apple has addressed the certificate validation issues within the Mail application. System administrators should implement mandatory certificate installation policies for all users who handle sensitive email communications, ensuring that proper S/MIME certificates are installed and configured in the keychain. Organizations should also consider implementing additional email security controls such as email encryption gateways or third-party email security solutions that can provide additional layers of protection. Regular security awareness training should emphasize the importance of certificate management and the risks associated with improper cryptographic configuration in email systems. Additionally, network monitoring solutions should be employed to detect unusual email traffic patterns that might indicate exploitation attempts targeting this vulnerability, particularly focusing on encrypted email traffic that shows signs of decryption bypass attempts.