A significant security flaw affecting Docker Sandboxes on macOS has been identified, allowing malicious code within a virtual machine to access host files. This vulnerability, detailed by Docker on September 15, poses a critical risk to systems running versions 0.28.0 up to but not including 0.42.0. The issue was addressed with the release of version 0.42.0 on September 7.
Understanding the Docker Vulnerability
The flaw, known as CVE-2026-77179, permits code running in a Docker Sandbox to escape its designated directory and access or modify files on the host system. This means any malicious code executed within the virtual machine gains the permissions of the host account. The vulnerability is considered critical, with a CVSS score of 9.4, and primarily affects macOS users.
While no instances of exploitation have been reported, both Docker and the Cybersecurity and Infrastructure Security Agency (CISA) have acknowledged the flaw. CISA’s records indicate no known exploitation, and the vulnerability is absent from its Known Exploited Vulnerabilities catalog as of September 16.
Technical Details and Implications
The flaw exploits the virtio-fs host server, which facilitates file sharing between the host and the virtual machine. By manipulating symlinks, a malicious guest could potentially execute code on the host. Docker’s documentation previously stated that symlinks outside the shared directory would not be followed, yet this vulnerability challenges that assurance.
In addition to CVE-2026-77179, another vulnerability, CVE-2026-79994, was identified. Rated as high severity with a CVSS score of 8.7, it impacts the Unix socket relay in versions 0.37.0 through 0.41.9. This flaw could allow unauthorized access to Unix sockets outside the workspace, compromising host-side capabilities.
Recommended Actions and Future Outlook
To mitigate these vulnerabilities, Docker advises users to upgrade to version 0.42.0 or later. The latest release, version 0.43.0, was made available on September 15. For those unable to update immediately, Docker suggests using clone mode to limit host file exposure. This mode ensures that the project directory is mounted read-only, offering some protection against unauthorized modifications.
Both vulnerabilities underscore the importance of regular software updates and adherence to security best practices. As Docker continues to improve its sandboxing technology, users are encouraged to stay informed about potential threats and apply updates promptly to safeguard their systems.
