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

CVE-2026-23518 → View on GitHub ↗ View on CVE.org ↗ View on NVD ↗

Description

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 [email protected]
Join #fleet in osquery Slack

Credits

We thank @secfox-ai for responsibly reporting this issue.

Basic information

Type
reviewed
Severity
critical
Advisory on GitHub
Open advisory ↗
Repository advisory
Open repository advisory ↗
Source code
Browse source ↗
Published (advisory)
2026-01-20 20:55:17 UTC
Updated
2026-03-27 17:38:46 UTC
GitHub reviewed
2026-01-20 20:55:17 UTC
NVD published
2026-01-21

EPSS Score

Score Percentile
0.05% 15.52%

CVSS Scores

Base score Version Severity Vector
9.3 4.0 —
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network.
Attack complexity (AC:L)
Exploitation conditions are straightforward and stable.
Attack requirements (AT:N)
No additional preconditions are required beyond normal reachability.
Privileges required (PR:N)
No privileges are required.
User interaction (UI:N)
No user interaction is required.
Vulnerable system confidentiality impact (VC:H)
High confidentiality impact on the vulnerable system.
Vulnerable system integrity impact (VI:H)
High integrity impact on the vulnerable system.
Vulnerable system availability impact (VA:H)
High availability impact on the vulnerable system.
Subsequent system confidentiality impact (SC:N)
No confidentiality impact on subsequent systems.
Subsequent system integrity impact (SI:N)
No integrity impact on subsequent systems.
Subsequent system availability impact (SA:N)
No availability impact on subsequent systems.

Identifiers

Type Value
GHSA GHSA-63m5-974w-448v ↗
CVE CVE-2026-23518 ↗

CWEs

CWE id Name
CWE-347 Improper Verification of Cryptographic Signature

Credits

  • prateek-0490 (reporter)
  • JordanMontgomery (remediation_developer)

Affected packages (5)

Vulnerable version ranges and first patched releases as published by GitHub.

Ecosystem Package Vulnerable range First patched Vulnerable functions
go github.com/fleetdm/fleet >= 4.78.0, < 4.78.3 4.78.3 —
go github.com/fleetdm/fleet >= 4.77.0, < 4.77.1 4.77.1 —
go github.com/fleetdm/fleet >= 4.76.0, < 4.76.2 4.76.2 —
go github.com/fleetdm/fleet >= 4.75.0, < 4.75.2 4.75.2 —
go github.com/fleetdm/fleet < 4.43.5-0.20260112202845-e225ef57912c 4.43.5-0.20260112202845-e225ef57912c —

References

cvelogic Threat Intelligence