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CVE-2026-72839 – Unauthenticated Privilege Escalation to Full Server Access – File Browser (filebrow

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Summary

CVE-2026-72839 is a critical privilege escalation vulnerability (CWE-266: Incorrect Privilege Assignment) in the open-source File Browser project (github.com/filebrowser/filebrowser/v2), affecting all versions through 2.63.16. When self-registration (signup) is enabled with the default CreateUserDir setting, any unauthenticated user who self-registers is granted a scope of the entire server root along with full file read, write, delete, rename, share, and download permissions. The issue carries a CVSS v3.1 base score of 9.8 (Critical), with IONIX recording a 9.3 severity for this advisory.

Technical details

  • Root cause: When signup is enabled, newly created accounts only have Admin, Execute, and Commands privileges stripped — six other destructive permissions (create, modify, delete, rename, share, download) remain granted by default.
  • Trigger condition: The vulnerability requires Signup=true and the default CreateUserDir=false configuration. In this state, new self-registered accounts receive Scope="/", i.e., the entire directory tree served by the application, instead of a restricted per-user directory.
  • Attack vector: Network-based and requires no authentication or user interaction — an attacker simply registers a new account through the exposed signup form.
  • Impact: A newly registered, unauthenticated attacker can read all files on the server (including other users’ data and secrets), create or modify arbitrary files, delete any file causing data loss, and break multi-tenant isolation in shared deployments.

Affected software

  • filebrowser/filebrowser (File Browser), all versions from the initial release through 2.63.16, when self-signup is enabled with default CreateUserDir settings.

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical) — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  • CVSS v4.0: 9.3 (Critical) — 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

Mitigation and recommended actions

  • Immediate: Upgrade to File Browser v2.63.17 or later, which adds a startup warning when signup is enabled without proper directory isolation.
  • Configuration mitigation (required even after upgrading): Disable self-signup (Signup=false) unless strictly necessary. If signup must remain enabled, enable CreateUserDir so each new account is confined to its own restricted directory rather than the server root, and review/restrict default permissions and scope assigned to new accounts.
  • Additional hardening: Audit existing user accounts and scopes created while signup was misconfigured, and rotate any secrets that may have been exposed to unauthorized users.

References

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