CVE-2026-23998: Fleet has a Windows MDM management endpoint authentication bypass
Summary
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.
Impact
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.
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.
Other sources
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.
— MITRE
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-23998?
CVE-2026-23998 has a high severity due to its potential to allow unauthorized access to sensitive configuration data.
What are the potential risks associated with CVE-2026-23998?
CVE-2026-23998 could enable an attacker to impersonate enrolled Windows devices, leading to the exposure of sensitive information.
How do I fix CVE-2026-23998?
To fix CVE-2026-23998, upgrade to Fleet version 4.81.0 or later where the client certificate validation is properly implemented.
Which versions of Fleet are affected by CVE-2026-23998?
CVE-2026-23998 affects Fleet versions prior to 4.81.0.
Is there a workaround for CVE-2026-23998?
Currently, the recommended action for CVE-2026-23998 is to update to the latest version, as there are no specific workarounds provided.