Fleet vulnerable to OS command injection in software packages

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.0 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-26191: 0.77% estimated exploitation activity in the next 30 days; percentile 55.75 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary A vulnerability in Fleet's software installer pipeline could allow a crafted software package to execute arbitrary commands as root (macOS/Linux) or SYSTEM (Windows) on managed endpoints when an uninstall is triggered. Impact When a software package (.pkg, .deb, .rpm, .exe, or .msi) is uploaded to Fleet, metadata is extracted from the package binary and used to generate uninstall scripts. In affected versions, this metadata is not properly sanitized before being included in the generated scripts. A specially crafted package containing malicious values in its metadata fields could result in unintended command execution when the uninstall script runs on managed endpoints. Workarounds If an immediate upgrade is not possible, administrators should avoid uploading software packages obtained from untrusted or unverified sources. Additionally, administrators can manually inspect and edit auto-generated uninstall scripts before deployment. For more information If you have any…

Published by the source

14 May 2026, 13:17 UTC

Last modified by the source

15 May 2026, 23:45 UTC

Source last checked

26 Oct 2026, 15:22 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-9vcr-g537-3w5v

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# Patch Next advisory brief: CVE-2026-26191

Advisory: Fleet vulnerable to OS command injection in software packages
IDs: CVE-2026-26191, GHSA-9vcr-g537-3w5v
Record: https://patchnext.com/advisories/cve-2026-26191 (revision 1, source checked 26 Oct 2026, 15:22 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.0)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/fleetdm/fleet/v4 4.81.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/fleetdm/fleet/v4: affected < 4.81.1; fixed in 4.81.1

## Suggested inspection (read-only)
- Go github.com/fleetdm/fleet/v4: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/fleetdm/fleet/v4.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-9vcr-g537-3w5v (GitHub-reviewed advisory GHSA-9vcr-g537-3w5v lists affected ranges: Go github.com/fleetdm/fleet/v4 >=0 <4.81.1)

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