CVE-2026-23518: Fleet has a JWT signature bypass vulnerability in Azure AD MDM enrollment
Summary
A vulnerability in Fleet’s Windows MDM enrollment flow could allow an attacker to submit forged authentication tokens that are not properly validated. Because JWT signatures were not verified, Fleet could accept attacker-controlled identity claims, enabling enrollment of unauthorized devices under arbitrary Azure AD user identities.
Impact
If Windows MDM is enabled, an attacker can enroll rogue devices by submitting a forged JWT containing arbitrary identity claims. Due to missing JWT signature verification, Fleet accepts these claims without validating that the token was issued by Azure AD, allowing enrollment under any Azure AD user identity.
Patches
- 4.78.3 - 4.77.1 - 4.76.2 - 4.75.2 - 4.53.3
Workarounds
If an immediate upgrade is not possible, affected Fleet users should temporarily disable Windows MDM.
For more information
If you have any questions or comments about this advisory:
Email us at security@fleetdm.com Join #fleet in osquery Slack
Credits
We thank @secfox-ai for responsibly reporting this issue.
Other sources
Fleet is open source device management software. In versions prior to 4.78.3, 4.77.1, 4.76.2, 4.75.2, and 4.53.3, a vulnerability in Fleet's Windows MDM enrollment flow could allow an attacker to submit forged authentication tokens that are not properly validated. Because JWT signatures were not verified, Fleet could accept attacker-controlled identity claims, enabling enrollment of unauthorized devices under arbitrary Azure AD user identities. Versions 4.78.3, 4.77.1, 4.76.2, 4.75.2, and 4.53.3 fix the issue. If an immediate upgrade is not possible, affected Fleet users should temporarily disable Windows MDM.
— MITRE
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2026-23518?
CVE-2026-23518 is classified as a critical vulnerability due to its potential to allow unauthorized access through forged JWT tokens.
How do I fix CVE-2026-23518?
To fix CVE-2026-23518, update to Fleet version 4.43.5-0.20260112202845-e225ef57912c or any version between 4.75.0 to 4.78.3.
What are the potential impacts of CVE-2026-23518?
The potential impacts of CVE-2026-23518 include unauthorized data access and compromised user accounts due to inadequate JWT signature validation.
Which versions of Fleet are affected by CVE-2026-23518?
CVE-2026-23518 affects Fleet versions prior to 4.43.5-0.20260112202845-e225ef57912c as well as versions 4.75.0 to 4.78.2.
Is there a workaround for CVE-2026-23518?
There are no recommended workarounds for CVE-2026-23518, and the best course of action is to apply the appropriate updates.