Fleet's macOS app install and uninstall scripts generated from Homebrew cask metadata before 2026-08-19 improperly neutralized special shell characters at some interpolation sites. This allowed crafted metadata containing shell metacharacters (e.g., command substitution) to be included in scripts executed as root on managed hosts, leading to OS command injection. Exploitation requires an attacker to insert malicious metadata into an upstream Homebrew cask and have it pass both upstream and Fleet's ingestion reviews. The vulnerability was addressed by fully escaping all cask metadata interpolation sites starting 2026-08-19, with the fix deployed centrally and included in Fleet v4.92.0.

An attacker who can insert crafted metadata into an upstream Homebrew cask could achieve arbitrary command execution as root on managed macOS hosts during app install or uninstall operations. This could lead to full system compromise on affected hosts. However, exploitation requires the malicious metadata to pass both upstream Homebrew cask review and Fleet's ingestion pipeline review, which limits the attack surface. The vulnerability has a high CVSS 4.0 score of 8.9.

The vulnerability was fixed on 2026-08-19 by fully escaping all cask metadata in Fleet's script generation pipeline. This fix was deployed centrally and included in Fleet version 4.92.0. Because manifests are generated centrally and distributed as pre-built content, remediation was applied automatically with no customer action required. Users should ensure they are running Fleet v4.92.0 or later to benefit from the fix.