CVE-2026-23518 Fleet has a JWT signature bypass vulnerability in Azure AD MDM enrollment
Attackers can forge JWT tokens to enroll unauthorized devices under arbitrary user identities due to missing signature verification in Fleet's Windows MDM enrollment.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-23518?
CVE-2026-23518 is a critical authentication bypass vulnerability in fleetdm fleet, published on 21 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-347
Which versions are affected by CVE-2026-23518?
11 open source packages ship an affected version, including github.com/fleetdm/fleet and github.com/fleetdm/fleet/v4. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/fleetdm/fleet Go | All versions | 4.43.5-0.20260112202845-e225ef57912c |
github.com/fleetdm/fleet Go | All versions | 4.43.5-0.20260112202845-e225ef57912c |
github.com/fleetdm/fleet Go | From 4.75.0 | 4.75.2 |
github.com/fleetdm/fleet Go | From 4.75.0 | 4.75.2 |
github.com/fleetdm/fleet Go | From 4.76.0 | 4.76.2 |
github.com/fleetdm/fleet Go | From 4.76.0 | 4.76.2 |
5 more packages
github.com/fleetdm/fleet Go | From 4.77.0 | 4.77.1 |
github.com/fleetdm/fleet Go | From 4.77.0 | 4.77.1 |
github.com/fleetdm/fleet Go | From 4.78.0 | 4.78.3 |
github.com/fleetdm/fleet Go | From 4.78.0 | 4.78.3 |
github.com/fleetdm/fleet/v4 Go | From 4.75.0 | 4.75.2, 4.76.2, 4.77.1, 4.78.3 |
Products include Fleetdm Fleet.
How do I fix CVE-2026-23518?
Upgrade github.com/fleetdm/fleet to a fixed version for your release line: 4.43.5-0.20260112202845-e225ef57912c, 4.75.2, 4.76.2 or 4.77.1.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-23518 being exploited?
There is no known exploitation of CVE-2026-23518 in the wild and no public exploit code.
Other vulnerabilities in fleetdm fleet
- CVE-2020-26276 SAML authentication vulnerability in Fleet
- CVE-2026-103264 Fleet before 4.87.0 Authentication Bypass via Device Identifiers
- CVE-2026-26062 Fleet server may terminate unexpectedly when handling certain gRPC requests
- CVE-2026-26061 Fleet's unbounded request body read allows remote Denial of Service
- CVE-2026-23998 Fleet has a Windows MDM management endpoint authentication bypass
Sources
Also known as GHSA-63m5-974w-448v, GO-2026-4335.