CVE-2026-23998: Github.com/fleetdm/fleet/v4 Authentication Bypass Vulnerability
HIGHCVE-2026-23998 is a HIGH (CVSS 7.5) authentication bypass vulnerability (CWE-295: Improper Certificate Validation) affecting Github.com/fleetdm/fleet/v4 libraries in the Go ecosystem. The issue involves fleet has a windows mdm management endpoint authentication bypass. Remediation is available by upgrading affected packages to version 4.81.0.
CVE-2026-23998 at a Glance
Security Impact
CVSS: 7.5
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N).
How to Fix CVE-2026-23998
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 4.81.0Run 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-2026-23998, 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 4.81.0), 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-295: Improper Certificate Validation, where the product does not validate, or incorrectly validates, a certificate. 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-2026-23998 Affected Github.com/fleetdm/fleet/v4 Versions
1 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
github.com/fleetdm/fleet/v4
|
Go |
< 4.81.0
|
4.81.0
|
References
Frequently Asked Questions
What is CVE-2026-23998?
Which Github.com/fleetdm/fleet/v4 versions are affected?
What version fixes CVE-2026-23998?
Is github.com/fleetdm/fleet/v4 affected?
What is the CVSS score of CVE-2026-23998?
What CWE is associated with CVE-2026-23998?
How can I check Go dependencies for CVE-2026-23998?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-2rc4-7jc6-qffh",
"modified" : "2026-06-08T23:36:07Z",
"published" : "2026-05-14T13:13:11Z",
"aliases" : [ "CVE-2026-23998" ],
"summary" : "Fleet has a Windows MDM management endpoint authentication bypass",
"details" : "### Summary\n\nA vulnerability in Fleet’s Windows MDM management endpoint could allow requests to be processed without proper client certificate validation. In certain circumstances, this could allow an attacker to impersonate an enrolled Windows device and retrieve sensitive configuration data.\n\n### Impact\n\nFleet’s Windows MDM management endpoint relies on mutual TLS (mTLS) client certificates to authenticate enrolled devices. In affected versions, requests that did not present a client certificate could be incorrectly treated as trusted.\n\nAs a result, an attacker with prior knowledge of a valid enrolled device identifier could potentially impersonate that device and receive configuration payloads intended for it. These payloads may contain sensitive information such as Wi-Fi or VPN configuration data, certificates, or other secrets delivered through MDM profiles.\n\nThis issue does not allow enrollment of new devices, administrative access to Fleet, or compromise of the Fleet control plane. Impact is limited to the targeted Windows device.\n\n### Workarounds\n\nIf an immediate upgrade is not possible, affected Fleet users should temporarily disable Windows MDM.\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)\nJoin #fleet in [osquery Slack](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_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"
}, {
"type" : "CVSS_V4",
"score" : "CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:N/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" : "4.81.0"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/fleetdm/fleet/security/advisories/GHSA-2rc4-7jc6-qffh"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-23998"
}, {
"type" : "WEB",
"url" : "https://github.com/fleetdm/fleet/commit/3ff8119ab8f794806a4cc82e21f760c123d92966"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/fleetdm/fleet"
}, {
"type" : "WEB",
"url" : "https://github.com/fleetdm/fleet/releases/tag/fleet-v4.81.0"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-295" ],
"severity" : "HIGH",
"github_reviewed" : true,
"github_reviewed_at" : "2026-05-14T13:13:11Z",
"nvd_published_at" : "2026-05-14T19:16:30Z"
}
}