CVE-2026-23518: Fleet has a JWT signature bypass vulnerability in Azure AD MDM enrollment

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-01-21 · updated 2026-06-17
Weakness: CWE-347

Description

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.

Affected products

fleetdm fleet: before 4.53.3; from 4.75.0 before 4.75.2; from 4.76.0 before 4.76.2; from 4.78.0 before 4.78.3; 4.77.0 — fixed in 4.53.3, 4.75.2, 4.76.2, 4.78.3

How to fix

Upgrade to a fixed version: fleetdm fleet 4.53.3, 4.75.2, 4.76.2, 4.78.3. Check the vendor advisory for mitigations.

References

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