Fleet Windows MDM endpoint has a Cross-site Scripting vulnerability

Summary

fleetdm/fleet is open source device management software. Prior to versions 4.78.2, 4.77.1, 4.76.2, 4.75.2, and 4.53.3, if Windows MDM is enabled, an unauthenticated attacker can exploit this XSS vulnerability to steal a Fleet administrator's authentication token (FLEET::auth_token) from localStorage. This could allow unauthorized access to Fleet, including administrative access, visibility into device data, and modification of configuration. Versions 4.78.2, 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.

Timeline

1. Jan 21, 2026, 9:18 PM UTCCVE published
2. Jan 22, 2026, 3:09 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Jan 22, 2026, 4:50 PM UTCRecord last updated

Affected versions

• fleetdm fleet

  From 4.78.0 · fixed in 4.78.2; From 4.77.0 · fixed in 4.77.1; From 4.76.0 · fixed in 4.76.2; fixed in 4.53.3

• github.com/fleetdm/fleetGo

  From 4.78.0 · fixed in 4.78.2

• github.com/fleetdm/fleetGo

  From 4.77.0 · fixed in 4.77.1

• github.com/fleetdm/fleetGo

  From 4.76.0 · fixed in 4.76.2

• github.com/fleetdm/fleetGo

  From 4.75.0 · fixed in 4.75.2

• github.com/fleetdm/fleet/v4Go

  fixed in 4.43.5-0.20260111020427-0e6c790803d1

• github.com/fleetdm/fleet/v4Go

  From 4.75.0 · fixed in 4.75.2; From 4.76.0 · fixed in 4.76.2; From 4.77.0 · fixed in 4.77.1; From 4.78.0 · fixed in 4.78.2

References 1