CVE-2026-24899: Fleet Windows MDM Azure AD JWT Authentication Bypass
Summary
A vulnerability in Fleet's Windows MDM enrollment flow allows authentication tokens from any Azure AD tenant to be accepted. Because Fleet validates JWT signatures using Microsoft's multi-tenant JWKS endpoint but does not enforce the aud (audience) or iss (issuer) claims, any Microsoft-signed Azure AD access token containing the expected scopes can be used to authenticate to Fleet's MDM endpoints.
Impact
If Windows MDM is enabled, an attacker with access to any Azure AD tenant can obtain a valid Microsoft-signed token and use it to enroll unauthorized devices and interact with Fleet's MDM management APIs. During device management, Fleet may expose sensitive enrollment secrets embedded in MDM command payloads, enabling further unauthorized access.
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 @zaddy6 for responsibly reporting this issue.
Other sources
Fleet is open source device management software. Prior to version 4.82.0, a vulnerability in Fleet's Windows MDM enrollment flow allows authentication tokens from any Azure AD tenant to be accepted. Because Fleet validates JWT signatures using Microsoft's multi-tenant JWKS endpoint but does not enforce the aud (audience) or iss (issuer) claims, any Microsoft-signed Azure AD access token containing the expected scopes can be used to authenticate to Fleet's MDM endpoints. If Windows MDM is enabled, an attacker with access to any Azure AD tenant can obtain a valid Microsoft-signed token and use it to enroll unauthorized devices and interact with Fleet's MDM management APIs. During device management, Fleet may expose sensitive enrollment secrets embedded in MDM command payloads, enabling further unauthorized access. Version 4.82.0 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-2026-24899?
CVE-2026-24899 is classified as a high-severity vulnerability due to its potential to allow unauthorized access to systems using flawed authentication mechanisms.
How do I fix CVE-2026-24899?
To fix CVE-2026-24899, upgrade to Fleet version 4.82.0 or later where the JWT signature verification process has been strengthened.
What systems are affected by CVE-2026-24899?
CVE-2026-24899 affects versions prior to 4.82.0 of Fleet's Windows MDM enrollment flow.
What is the impact of CVE-2026-24899?
The impact of CVE-2026-24899 allows authentication tokens from any Azure AD tenant, potentially leading to unauthorized actions on the affected systems.
Is CVE-2026-24899 related to JWT validation?
Yes, CVE-2026-24899 is related to improper validation of JWT signatures, specifically lacking enforcement of the 'aud' and 'iss' claims.