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CVE-2026-103264 – Authentication Bypass – Fleet (fleetdm) before 4.87.0

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Summary

CVE-2026-103264 is a critical authentication bypass vulnerability in Fleet, the open-source device management (MDM) platform from fleetdm, affecting all versions prior to 4.87.0. The flaw resides in Fleet’s device API, which improperly accepts hostnames and hardware serial numbers as valid authentication tokens alongside the intended device UUID. Because hostnames and hardware serials are not secret values, an unauthenticated attacker who learns or guesses one can impersonate an enrolled iOS/iPadOS device and access its data or trigger device-scoped actions.

Technical details

  • Root cause: The device API’s authentication logic treats hostname and hardware serial as interchangeable with the device UUID when validating the bearer-style device token, even though these identifiers are not kept secret and can often be discovered or guessed.
  • Trigger conditions: An attacker only needs to know (or guess) the hostname or hardware serial of an iOS/iPadOS device enrolled in a vulnerable Fleet server.
  • Attack vector: Network-based; no authentication or user interaction is required (CWE-287: Improper Authentication).
  • Impact: Successful exploitation allows an attacker to authenticate as the targeted device, read device information, and execute device-scoped operations such as software installation/deployment and MDM migration — all without valid credentials.

Affected software

  • Fleet (fleetdm) — all versions prior to 4.87.0
  • Fixed in Fleet 4.87.0 and later

Severity

  • CVSS v3.1 Base Score: 9.1 (Critical) — Vector: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
  • A CVSS v4.0 score of 9.3 (Critical) has also been published for this issue.

Mitigation and recommended actions

  • Immediate: Upgrade Fleet to version 4.87.0 or later, where hostname/hardware-serial values are no longer accepted as device API authentication tokens.
  • If immediate patching is not possible: Restrict network exposure of the Fleet device API endpoint to trusted networks only, monitor device API access logs for requests using recognizable hostnames or serial numbers as tokens, and treat all enrolled device hostnames/serials as sensitive values pending upgrade.

References

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