OS Command Injection in github.com/fleetdm/fleet/v4 (CVE-2026-26191)
Summary
OS command injection in github.com/fleetdm/fleet/v4 (CVE-2026-26191). Successful exploitation can lead to full system takeover. Mitigation: upgrade to 4.81.1 or later.
Original description
The description as published by the source.
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 questions or comments about this advisory:
Email us at [security@fleetdm.com](mailto:security@fleetdm.com)
Join #fleet in [osquery Slack](https://join.slack.com/t/osquery/shared_invite/zt-h29zm0gk-s2DBtGUTW4CFel0f0IjTEw)
Credits
We thank @secfox-ai for responsibly reporting this issue.
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-26191 has been found in github.com/fleetdm/fleet/v4.
Successful exploitation can lead to full system takeover. CVSS score: 9.8/10.
What to do: upgrade github.com/fleetdm/fleet/v4 to 4.81.1 or later.
If unsure, ask your IT team or search "github.com/fleetdm/fleet/v4 CVE-2026-26191" on the vendor's site.
CVE-2026-26191 (github.com/fleetdm/fleet/v4) — CWE-78 / CVSS v3 9.8
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 4.81.1 — apply immediately
Workaround: If an immediate upgrade is not possible, administrators should avoid uploading software packages obtained from untrusted or unverified sources.
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
OS command injection (CWE-78) exists in github.com/fleetdm/fleet/v4.
Check the vendor advisory for the affected versions of github.com/fleetdm/fleet/v4.
Severity: Critical (CVSS 9.8/10). Successful exploitation can lead to full system takeover.
Update to 4.81.1.
Workaround: If an immediate upgrade is not possible, administrators should avoid uploading software packages obtained from untrusted or unverified sources.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'github.com/fleetdm/fleet/v4' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'github.com/fleetdm/fleet/v4' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
github.com/fleetdm/fleet/v4を grep し、稼働しているサービス・バージョンを把握する。 -
2Apply temporary workaround mitigate
If an immediate upgrade is not possible, administrators should avoid uploading software packages obtained from untrusted or unverified sources.パッチが適用されるまでの応急処置として、If an immediate upgrade is not possible, administrators should avoid uploading software packages obtained from untrusted or unverified sources. を実施。回避策の副作用 (機能低下) を確認した上で。
-
3Apply patch patch
Upgrade github.com/fleetdm/fleet/v4 to 4.81.1ステージング環境で 4.81.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
4Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory nvd.nist.gov
- package github.com
- web github.com
- web github.com
- web github.com