CVE-2019-6239 in macOS
Summary
by MITRE
This issue was addressed with improved handling of file metadata. This issue is fixed in macOS Mojave 10.14.4. A malicious application may bypass Gatekeeper checks.
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Analysis
by VulDB Data Team • 05/21/2020
CVE-2019-6239 represents a significant security vulnerability in Apple's macOS operating system that specifically targeted the Gatekeeper protection mechanism. This flaw allowed malicious applications to bypass critical security checks designed to prevent unauthorized software execution. The vulnerability was classified as a privilege escalation issue that could be exploited by attackers to circumvent the operating system's built-in security controls. The problem stemmed from inadequate handling of file metadata during the verification process, creating a pathway for malicious actors to manipulate the system's trust model. This issue directly impacted the core security architecture of macOS by undermining the fundamental principle of code signing verification that Gatekeeper relies upon for protecting users from potentially harmful applications.
The technical exploitation of CVE-2019-6239 occurred through manipulation of file metadata attributes that Gatekeeper uses to validate application authenticity. Attackers could craft malicious applications with carefully modified metadata that would pass the Gatekeeper validation process despite being unsigned or improperly signed. This vulnerability exploited the gap between the metadata verification process and the actual code execution checks, allowing attackers to insert malicious code into the system while appearing legitimate to the operating system's security mechanisms. The flaw was particularly dangerous because it leveraged the system's own validation logic against itself, making detection more difficult and exploitation more effective. This type of vulnerability aligns with CWE-284, which addresses improper access control, and demonstrates how metadata handling issues can create security gateways in system protection mechanisms.
The operational impact of CVE-2019-6239 was substantial as it effectively neutralized one of macOS's primary defense mechanisms against unauthorized software execution. Organizations and individual users who were running affected versions of macOS were vulnerable to attacks that could result in full system compromise without the typical security warnings or user prompts that Gatekeeper normally provides. This vulnerability particularly affected environments where security was paramount, as it allowed attackers to bypass the security controls that would normally prevent the installation and execution of unknown applications. The exploitation could lead to data theft, system corruption, or the installation of additional malware, making it a critical concern for enterprise security teams and individual users alike. The vulnerability demonstrated how subtle flaws in system metadata handling could create significant security risks.
Apple addressed CVE-2019-6239 through the release of macOS Mojave 10.14.4, which included enhanced metadata validation procedures that corrected the flaw in Gatekeeper's verification process. The fix implemented improved checks for file metadata attributes and strengthened the validation logic to prevent manipulation of these critical security elements. Organizations should have immediately applied this update to protect their systems from exploitation attempts. Additional mitigations included implementing network-based security controls, monitoring for suspicious application installations, and ensuring that only trusted applications were executed on affected systems. The vulnerability highlighted the importance of continuous security updates and the need for organizations to maintain robust patch management procedures. Security professionals should have monitored for exploitation attempts and implemented additional controls to protect against potential attacks that could leverage this flaw in systems that had not yet been updated. This vulnerability underscored the critical role of metadata integrity in system security and the necessity of comprehensive validation procedures.