CVE-2026-101045 in Fleet
Summary
by MITRE • 09/27/2026
Fleet-maintained app install and uninstall scripts for macOS are generated from Homebrew cask metadata. In manifests generated before 2026-08-19, the script generator escaped this metadata at some interpolation sites but not all of them, so cask metadata containing shell metacharacters (for example $(...) command substitution) could be carried into scripts that execute as root on managed macOS hosts. An attacker who could land crafted metadata in an upstream Homebrew cask — without needing any Fleet credentials — could achieve arbitrary command execution as root on managed macOS hosts that install or uninstall the affected Fleet-maintained app; exploitation required the crafted metadata to pass both upstream Homebrew cask review and Fleet's review of the automated ingestion pull request. The fix (fleetdm/fleet#51324) landed in Fleet's ingestion pipeline on 2026-08-19 so that all manifests generated on or after that date escape cask metadata at every interpolation site; because manifests are generated centrally and distributed as pre-built content, remediation applied to all deployments with no customer action, and the code fix is included in Fleet v4.92.0.
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Analysis
by VulDB Data Team • 09/27/2026
The vulnerability described involves a critical input validation failure within the automated script generation process of Fleet for macOS environments. Specifically, the system generates install and uninstall scripts based on metadata extracted from Homebrew casks to facilitate fleet-wide application management. In manifests generated prior to August 19, 2026, the sanitization logic was incomplete. While certain interpolation points in the template engine correctly escaped special characters, other critical sites were left unescaped. This inconsistency allowed shell metacharacters present within the Homebrew cask metadata to be injected directly into the resulting bash scripts without proper filtering or encoding.
The technical flaw centers on improper neutralization of special elements used in commands, which aligns with CWE-78: Improper Neutralization of Special Elements used in an OS Command. When a managed macOS host executes these Fleet-maintained app install or uninstall operations, the script runs with root privileges to ensure proper system-level changes are applied. Because the injection points were not fully sanitized, any shell metacharacters embedded in the metadata, such as command substitution syntax like $(...), would be interpreted by the shell during execution rather than treated as literal data. This creates a pathway for arbitrary code execution under the context of the root user on the target macOS host.
The operational impact is severe due to the privilege level at which the vulnerability operates. An attacker who successfully introduces crafted metadata into an upstream Homebrew cask can achieve remote command execution with full administrative privileges on any managed device that installs or uninstalls the affected application via Fleet. However, exploitation requires a multi-stage attack vector. The malicious payload must first pass the review process of the upstream Homebrew project and subsequently survive Fleet's automated ingestion pull request reviews. This implies that while the vulnerability is critical in terms of potential impact, it relies on social engineering or compromise of trusted software supply chains rather than direct network-based exploitation against the Fleet server itself.
Mitigation for this issue was implemented centrally within Fleet’s infrastructure rather than requiring individual customer action. The fix, identified as fleetdm/fleet#51324, was deployed to the ingestion pipeline on August 19, 2026. This update ensures that all manifests generated from that date onward properly escape cask metadata at every interpolation site, effectively closing the injection vector. Consequently, organizations using Fleet versions v4.92.0 or later are protected against this specific attack path without needing to manually patch individual endpoints or scripts. The remediation strategy leverages the centralized nature of fleet management tools to push corrected logic automatically to all managed hosts during their next synchronization cycle with the control plane.