CVE-2019-8656 in macOS
Summary
by MITRE • 10/28/2020
This was addressed with additional checks by Gatekeeper on files mounted through a network share. This issue is fixed in macOS Mojave 10.14.6, Security Update 2019-004 High Sierra, Security Update 2019-004 Sierra. Extracting a zip file containing a symbolic link to an endpoint in an NFS mount that is attacker controlled may bypass Gatekeeper.
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Analysis
by VulDB Data Team • 11/06/2023
The vulnerability described in CVE-2019-8656 represents a significant security flaw in macOS Gatekeeper protection mechanisms that specifically affects systems running macOS Mojave 10.14.5 and earlier versions. This issue arises from insufficient validation checks within Gatekeeper when processing files that are mounted through network shares, particularly NFS (Network File System) mounts. The vulnerability exploits a fundamental weakness in how the operating system handles symbolic links within compressed archives that are extracted from network locations, creating a pathway for malicious code execution that bypasses critical security controls.
The technical flaw stems from Gatekeeper's inadequate validation of symbolic links during archive extraction processes when files originate from network shares. When an attacker crafts a malicious zip file containing a symbolic link that points to an endpoint on a controlled NFS mount, the system fails to properly verify the target of the symbolic link before allowing the extraction process to proceed. This weakness allows the system to follow the symbolic link and potentially execute code from the attacker-controlled endpoint without proper Gatekeeper verification. The vulnerability specifically impacts the way macOS handles file system operations across network boundaries, where the traditional security checks that normally prevent unauthorized code execution are circumvented.
The operational impact of this vulnerability is substantial as it enables attackers to bypass Gatekeeper's core security protections that are designed to prevent the execution of unsigned or potentially malicious software. This allows adversaries to deliver malware through seemingly legitimate zip file attachments that contain symbolic links pointing to attacker-controlled network resources. The attack vector is particularly concerning because it leverages the trust relationships inherent in network file sharing protocols, making it difficult to distinguish between legitimate and malicious network operations. This vulnerability essentially undermines the principle of least privilege by allowing execution of code from network locations that should be subject to additional verification steps.
The mitigation strategy for CVE-2019-8656 involves updating to the patched versions of macOS, specifically macOS Mojave 10.14.6, and the corresponding Security Updates for High Sierra and Sierra. These updates implement additional validation checks within Gatekeeper to properly handle symbolic links during network share operations. Organizations should also implement network segmentation and monitoring to detect unusual symbolic link activity, particularly when extracting archives from network shares. The fix addresses the underlying issue by strengthening the validation logic to ensure that symbolic links are properly resolved and verified before any execution occurs, aligning with the principle of defense in depth as outlined in cybersecurity frameworks. This vulnerability demonstrates the importance of comprehensive input validation and proper access control mechanisms when dealing with network-based file operations, particularly in enterprise environments where network shares are commonly used. The fix implements controls consistent with CWE-22 (Improper Limitation of a Pathname to a Restricted Directory) and addresses attack patterns related to privilege escalation and code execution through trusted network pathways, as documented in MITRE ATT&CK framework under techniques involving execution through compromised network resources.