CVE-2026-23998

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.

Workarounds

If an immediate upgrade is not possible, affected Fleet users should temporarily disable Windows MDM.

For more information

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Credits

We thank @secfox-ai for responsibly reporting this issue.

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.

CVE-2026-23998 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.81.0); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-23998? CVE-2026-23998 is a high-severity security vulnerability in github.com/fleetdm/fleet/v4 (go), affecting versions < 4.81.0. It is fixed in 4.81.0.
2. How severe is CVE-2026-23998? CVE-2026-23998 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/fleetdm/fleet/v4 are affected by CVE-2026-23998? github.com/fleetdm/fleet/v4 (go) versions < 4.81.0 is affected.
4. Is there a fix for CVE-2026-23998? Yes. CVE-2026-23998 is fixed in 4.81.0. Upgrade to this version or later.
5. Is CVE-2026-23998 exploitable, and should I be worried? Whether CVE-2026-23998 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-23998 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-23998? Upgrade github.com/fleetdm/fleet/v4 to 4.81.0 or later.