What is CVE-2026-23998?

CVE-2026-23998 is a high-severity vulnerability in Fleetdm Fleet, classified under Improper Certificate Validation. CVSS score: 7.5/10. Published 2026-05-14.

How severe is CVE-2026-23998?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Fleetdm Fleet

CVE-2026-23998

Fleet is open source device management software. Prior to version 4.81.0, a 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. Fleet’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. As 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. This 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. Version 4.81.0 contains a patch. If an immediate upgrade is not possible, affected Fleet users should temporarily disable Windows MDM.

Vulnerability class: Improper Certificate Validation

Published 2026-05-14 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.

EPSS exploit prediction

EPSS: 0.002 (11.1th percentile), scored 2026-10-20.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 11th percentile — 11.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: 0.000

Affected products

Fleetdm Fleet — versions < 4.81.0

Weakness classification (CWE)

CWE-295 — Improper Certificate Validation

References

github.com/fleetdm/fleet/security/advisories/GHSA-2rc4-7jc6-qffh (Mitigation, Vendor Advisory)
github.com/fleetdm/fleet/releases/tag/fleet-v4.81.0 (Product, Release Notes)

Frequently asked questions

What is CVE-2026-23998?: CVE-2026-23998 is a high-severity vulnerability in Fleetdm Fleet, classified under Improper Certificate Validation. CVSS score: 7.5/10. Published 2026-05-14.
How severe is CVE-2026-23998?: High severity. CVSS v3 base score is 7.5 out of 10.