Fleet generates macOS app install scripts from Homebrew cask metadata. In manifests created before 2026-08-19 the script generator escaped some, but not all, interpolation points, allowing shell metacharacters in metadata to be injected into scripts that run with root privileges. This is an OS command injection vulnerability (CWE‑78). An attacker who can add crafted metadata to a Homebrew cask that passes both Homebrew and Fleet review could run arbitrary commands as root when a managed macOS host installs or uninstalls the affected Fleet‐maintained app.

The vulnerability affects macOS hosts managed by Fleet. Specifically, any Fleet deployment using manifests generated before 2026-08-19 is at risk, as these manifests may contain unescaped metadata. The fix was implemented in Fleet v4.92.0 on 2026-08-19 and applies centrally, so all deployments receive remediation without customer action.

The CVSS score of 8.9 indicates a high‐severity risk. The EPSS score is not available, and the vulnerability is not listed in CISA KEV, implying a lower public exploitation trend but still significant risk. Exploitation requires the attacker to insert malicious metadata into a Homebrew cask that passes both Homebrew’s cask review and Fleet’s ingestion review, then trigger an install or uninstall on a managed host. The payload then executes with root privileges on a macOS system, compromising confidentiality, integrity, and availability of that host.