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CVE-2026-86934 – Authorization Bypass / Unauthorized Data Access – Claris FileMaker Server (before 2

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Summary

CVE-2026-86934 is an authorization bypass vulnerability (CWE-639) in the Web Publishing Engine of Claris FileMaker Server. Affected versions fail to enforce the "Custom Web Publishing with XML" setting when it has been administratively disabled, allowing unauthenticated network requests that include a specially crafted extended privilege header to reach the XML Web Publishing interface anyway. The flaw carries a CVSS v3.1 base score of 9.1 (Critical) and requires no authentication or user interaction to exploit.

Technical details

  • Root cause: The Web Publishing Engine does not properly validate whether Custom Web Publishing with XML has been disabled before processing requests that present an extended privilege header, allowing the intended access control to be bypassed.
  • Trigger condition: An attacker sends a crafted HTTP request containing the extended privilege header directly to the XML Web Publishing interface, even when the administrator has explicitly disabled that publishing feature.
  • Attack vector: Network-based, low attack complexity, no privileges or user interaction required (AV:N/AC:L/PR:N/UI:N).
  • Impact: High impact to confidentiality and integrity — successful exploitation exposes database contents and interfaces via XML Web Publishing that were intended to be inaccessible, and may allow unauthorized data modification through that interface. There is no impact to availability.

Affected software

  • Claris FileMaker Server — all versions prior to 26.0.3

Severity

  • CVSS v3.1 Base Score: 9.1 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Mitigation and recommended actions

  • Immediate: Upgrade Claris FileMaker Server to version 26.0.3 or later, which corrects the authorization enforcement for the Web Publishing Engine.
  • If patching cannot be performed immediately:
    • Do not rely solely on the "Custom Web Publishing with XML" disabled setting as a security control — it does not fully block access on unpatched versions.
    • Restrict network access to the FileMaker Server Web Publishing Engine (including the XML Web Publishing interface) to trusted internal networks or VPN-only access using firewall/ACL rules.
    • Monitor Web Publishing Engine logs for requests containing unexpected extended privilege headers or anomalous XML Web Publishing access attempts.
    • Disable Custom Web Publishing entirely at the network layer (block external access to the relevant ports/paths) until the upgrade is completed.

References

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