CVE-2026-101045: Fleet macOS App Management RCE Vulnerability

CVE-2026-101045 Overview

CVE-2026-101045 is a command injection vulnerability [CWE-78] in Fleet's ingestion pipeline for Fleet-maintained macOS applications. The script generator pulled metadata from upstream Homebrew casks and escaped values at some interpolation sites but not all of them. Metadata containing shell metacharacters such as $(...) command substitution could be carried into install and uninstall scripts that execute as root on managed macOS hosts. An attacker who landed crafted metadata in an upstream Homebrew cask could achieve arbitrary command execution as root on affected endpoints without needing Fleet credentials.

Critical Impact
Successful exploitation yields arbitrary command execution as root on managed macOS hosts that install or uninstall an affected Fleet-maintained app, enabling full endpoint compromise across a managed fleet.

Affected Products

Fleet-maintained app manifests generated before 2026-08-19
Fleet versions prior to v4.92.0
Managed macOS hosts installing or uninstalling affected Fleet-maintained apps

Discovery Timeline

2026-08-19 - Fix landed in Fleet's ingestion pipeline (fleetdm/fleet#51324)
2026-09-27 - CVE-2026-101045 published to NVD
2026-09-30 - Last updated in NVD database

Technical Details for CVE-2026-101045

Vulnerability Analysis

Fleet generates install and uninstall scripts for Fleet-maintained macOS applications by templating values from upstream Homebrew cask manifests. The script generator applied shell escaping to several interpolation sites but missed others. Fields containing shell metacharacters, including command substitution syntax such as $(...), could flow unescaped into the generated scripts.

The generated scripts run with root privileges on managed macOS hosts as part of normal Mobile Device Management workflows. Any shell expression embedded in cask metadata executes in the context of that root shell during install or uninstall operations. The vulnerability is categorized as OS Command Injection [CWE-78].

Exploitation required the crafted metadata to pass both upstream Homebrew cask review and Fleet's review of the automated ingestion pull request. These review gates account for the high attack complexity, but a successful bypass would propagate to every deployment because manifests are generated centrally and distributed as pre-built content.

Root Cause

The root cause is inconsistent output encoding in the manifest generator. Shell escaping was applied at some interpolation sites but not at every site where cask metadata was embedded into the generated bash scripts. This gap allowed attacker-controlled strings to be interpreted as shell syntax rather than data.

Attack Vector

An attacker publishes a Homebrew cask with metadata fields containing shell metacharacters. If the cask passes upstream review and Fleet's automated ingestion pull request review, the generated script embeds the malicious metadata unescaped. When a managed macOS host runs the generated install or uninstall script, the embedded command substitution executes as root. The attacker does not need Fleet credentials or direct network access to the Fleet server.

See the GitHub Security Advisory and the VulnCheck Command Injection Advisory for the vendor disclosure.

Detection Methods for CVE-2026-101045

Indicators of Compromise

Unexpected child processes spawned by the Fleet orchestration agent (orbit or fleetd) on macOS hosts during software install or uninstall operations
Shell processes executing payloads sourced from install or uninstall script bodies that contain $(...) or backtick command substitution
Outbound network connections initiated by install or uninstall scripts to domains unrelated to the target application
New launch daemons, launch agents, or persistence artifacts created shortly after a Fleet-maintained app install event

Detection Strategies

Review manifests generated before 2026-08-19 for cask metadata fields containing shell metacharacters such as $, backticks, ;, |, or &&
Alert on root-level process creation chains originating from Fleet install or uninstall scripts that invoke curl, wget, osascript, bash -c, or sh -c with arguments not expected for a package install
Correlate Fleet software deployment events with endpoint telemetry to identify anomalous child processes during install windows

Monitoring Recommendations

Enable macOS Endpoint Security framework telemetry for process execution and file creation events on hosts enrolled in Fleet
Monitor Fleet's software library change log for additions or updates to Fleet-maintained apps and review the underlying cask metadata
Baseline the expected process tree for each Fleet-maintained app install and alert on deviations

How to Mitigate CVE-2026-101045

Immediate Actions Required

Confirm the Fleet server is running v4.92.0 or later, which includes the ingestion pipeline fix from fleetdm/fleet#51324
Verify that all Fleet-maintained app manifests in use were generated on or after 2026-08-19
Audit recent install and uninstall activity on managed macOS hosts for anomalous root process execution during the affected window

Patch Information

The code fix is included in Fleet v4.92.0. Because manifests are generated centrally by Fleet and distributed as pre-built content, remediation applied to all deployments automatically on 2026-08-19 with no customer action required. Upgrading to v4.92.0 ensures the ingestion pipeline cannot regenerate vulnerable manifests.

Workarounds

No manual workaround is required for manifests generated on or after 2026-08-19 because the central ingestion pipeline now escapes cask metadata at every interpolation site
For historical validation, review any locally cached or mirrored Fleet-maintained app scripts generated before 2026-08-19 and regenerate them from the current ingestion pipeline
Restrict which operators can approve Fleet-maintained app installs for sensitive device cohorts until auditing is complete

bash

# Verify Fleet server version meets the fixed release
fleetctl --version
# Expected: fleet version 4.92.0 or later