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CVE-2026-13439 – Unauthenticated Privilege Escalation to Administrator – Easy Form Builder by Whi…

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Summary

CVE-2026-13439 is a critical unauthenticated privilege escalation vulnerability in the Easy Form Builder by WhiteStudio WordPress plugin (versions up to and including 4.0.11), assigned a CVSS v3.1 score of 9.8. The flaw exists in the plugin’s password recovery flow, which exposes a publicly-visible session identifier as the effective password reset token and pairs it with an unauthenticated REST endpoint that freely issues valid WordPress nonces — enabling any remote attacker to reset any user’s password, including administrators, and achieve full site takeover without any prior credentials.

Technical details

  • Root cause: The password recovery mechanism stores a session identifier (sid) in the wp_emsfb_temp_links database table and embeds it visibly in published login form pages. This sid is then used as the authoritative password reset token, rather than a secret, single-use, out-of-band token.
  • Compounding weakness: The REST endpoint Emsfb/v1/nonce/refresh issues valid WordPress REST API nonces to completely unauthenticated visitors, removing the nonce-based access control that would otherwise gate subsequent requests.
  • Attack chain: An attacker (1) scrapes the publicly visible sid value from any page embedding the plugin’s login or recovery form; (2) submits a password recovery request for a target account — including administrator accounts — via the unauthenticated Emsfb/v1/forms/message/add REST endpoint; (3) calls Emsfb/v1/forms/recovery/efb_set_password with the known sid to set an arbitrary new password. No existing credentials, session cookie, or user interaction are required at any step.
  • Attack vector: Fully remote over the network (HTTP/HTTPS). No authentication, no user interaction, and no special site configuration beyond the plugin being installed and a login/recovery form being published.
  • Impact: Complete WordPress administrator account takeover — full confidentiality, integrity, and availability compromise of the affected site (C:H / I:H / A:H).

Affected software

  • Easy Form Builder by WhiteStudio – Drag & Drop Form Builder, all versions up to and including 4.0.11

Severity

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

Mitigation and recommended actions

  • Immediate — Update the plugin: The vulnerability is patched in version 4.0.12 and later. The current release available from WordPress.org is 4.1.1. All sites running version 4.0.11 or earlier should update immediately via the WordPress admin dashboard (Plugins → Updates) or by downloading the latest release from the official WordPress.org plugin repository.
  • If immediate patching is not possible: Temporarily deactivate the plugin to remove the vulnerable REST API endpoints from public exposure. Restrict access to WordPress REST API routes (/wp-json/Emsfb/v1/*) at the web server or WAF layer for unauthenticated requests until the plugin can be updated.
  • Post-remediation: Review WordPress administrator accounts and audit recent password changes or unexpected administrator additions for signs of prior exploitation.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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