GHSA-63m5-974w-448v: Fleet has a JWT signature bypass vulnerability in Azure AD MDM enrollment

1. GitHub Advisory Database
2. GitHub Reviewed
3. CVE-2026-23518

Fleet has a JWT signature bypass vulnerability in Azure AD MDM enrollment

Critical severity GitHub Reviewed Published Jan 20, 2026 in fleetdm/fleet • Updated Jan 20, 2026

Package

gomod github.com/fleetdm/fleet (Go)

Affected versions

>= 4.78.0, < 4.78.3

>= 4.77.0, < 4.77.1

>= 4.76.0, < 4.76.2

>= 4.75.0, < 4.75.2

< 4.43.5-0.20260112202845-e225ef57912c

Patched versions

4.78.3

4.77.1

4.76.2

4.75.2

4.43.5-0.20260112202845-e225ef57912c

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

References

• GHSA-63m5-974w-448v
• fleetdm/fleet@e225ef5

Published to the GitHub Advisory Database

Jan 20, 2026

Last updated

Jan 20, 2026