CVE-2026-26191: Github.com/fleetdm/fleet/v4 Fleet Vulnerable To OS Command Vulnerability
MODERATECVE-2026-26191 is a MODERATE fleet vulnerable to os command vulnerability (CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')) affecting Github.com/fleetdm/fleet/v4 libraries in the Go ecosystem. The issue involves fleet vulnerable to os command injection in software packages. Remediation is available by upgrading affected packages to version 4.81.1.
CVE-2026-26191 at a Glance
How to Fix CVE-2026-26191
To remediate this vulnerability, upgrade all affected Github.com/fleetdm/fleet/v4 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
Upgrade github.com/fleetdm/fleet/v4 to 4.81.1Run the following command in your project directory to verify that all resolved dependencies use the patched release:
inspect dependencies for github.com/fleetdm/fleet/v4How to Check if You Are Affected
To determine whether your application is affected by CVE-2026-26191, inspect your project dependencies for Github.com/fleetdm/fleet/v4:
inspect dependencies for github.com/fleetdm/fleet/v4Analyze the terminal output to locate any version of Github.com/fleetdm/fleet/v4 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.81.1), your application is affected.
Note: Verify declared build manifests and deployed runtime container environments.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection'), where the product constructs all or part of an os command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended os command when it is sent to a downstream component. In Github.com/fleetdm/fleet/v4, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
CVE-2026-26191 Affected Github.com/fleetdm/fleet/v4 Versions
1 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
github.com/fleetdm/fleet/v4
|
Go |
< 4.81.1
|
4.81.1
|
References
Frequently Asked Questions
What is CVE-2026-26191?
Which Github.com/fleetdm/fleet/v4 versions are affected?
What version fixes CVE-2026-26191?
Is github.com/fleetdm/fleet/v4 affected?
What CWE is associated with CVE-2026-26191?
How can I check Go dependencies for CVE-2026-26191?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-9vcr-g537-3w5v",
"modified" : "2026-05-15T23:45:34Z",
"published" : "2026-05-14T13:17:36Z",
"aliases" : [ "CVE-2026-26191" ],
"summary" : "Fleet vulnerable to OS command injection in software packages",
"details" : "### Summary\n\nA 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.\n\n### Impact\n\nWhen 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.\n\n### Workarounds\n\nIf 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.\n\n### For more information\n\nIf you have any questions or comments about this advisory:\n\nEmail us at [[security@fleetdm.com](mailto:security@fleetdm.com)](mailto:security@fleetdm.com)\n\nJoin #fleet in [[osquery Slack](https://join.slack.com/t/osquery/shared_invite/zt-h29zm0gk-s2DBtGUTW4CFel0f0IjTEw)](https://join.slack.com/t/osquery/shared_invite/zt-h29zm0gk-s2DBtGUTW4CFel0f0IjTEw)\n\n### Credits\n\nWe thank @secfox-ai for responsibly reporting this issue.",
"severity" : [ {
"type" : "CVSS_V4",
"score" : "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"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "Go",
"name" : "github.com/fleetdm/fleet/v4"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "4.81.1"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/fleetdm/fleet/security/advisories/GHSA-9vcr-g537-3w5v"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-26191"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/fleetdm/fleet"
}, {
"type" : "WEB",
"url" : "https://github.com/fleetdm/fleet/releases/tag/fleet-v4.81.1"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-78" ],
"severity" : "MODERATE",
"github_reviewed" : true,
"github_reviewed_at" : "2026-05-14T13:17:36Z",
"nvd_published_at" : "2026-05-14T20:17:02Z"
}
}