JWT Signature Bypass in Fleet Windows MDM Enables Unauthorized Enrollment

Publication date: 2026-01-21

Last updated on: 2026-02-27

Assigner: GitHub, Inc.

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.

CVSS Scores

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Meta Information

Published

2026-01-21

Last Modified

2026-02-27

Generated

2026-07-06

AI Q&A

2026-01-22

EPSS Evaluated

2026-07-05

NVD

CVE-2026-23518

Affected Vendors & Products

Vendor	Product	Version / Range
fleetdm	fleet	to 4.53.3 (exc)
fleetdm	fleet	From 4.75.0 (inc) to 4.75.2 (exc)
fleetdm	fleet	From 4.76.0 (inc) to 4.76.2 (exc)
fleetdm	fleet	4.77.0
fleetdm	fleet	From 4.78.0 (inc) to 4.78.3 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-347	The product does not verify, or incorrectly verifies, the cryptographic signature for data.

Attack-Flow Graph

Executive Summary

This vulnerability exists in Fleet's Windows MDM enrollment flow where attacker-submitted forged authentication tokens are not properly validated. Specifically, JWT signatures were not verified, allowing attackers to submit attacker-controlled identity claims. This flaw enables unauthorized devices to be enrolled under arbitrary Azure AD user identities.

Impact Analysis

The vulnerability can allow attackers to enroll unauthorized devices into the Fleet device management system under any Azure AD user identity. This could lead to unauthorized access, potential data breaches, and compromise of managed devices.

Mitigation Strategies

If an immediate upgrade to fixed versions (4.78.3, 4.77.1, 4.76.2, 4.75.2, or 4.53.3) is not possible, affected Fleet users should temporarily disable Windows MDM enrollment to mitigate the vulnerability.

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