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Advanced Custom Fields: Extended Plugin Vulnerability (CVE-2026-8809)

Nick Paliughi
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Security Alert Summary

The Advanced Custom Fields: Extended plugin for WordPress has a privilege escalation vulnerability (CVE-2026-8809) that can allow an attacker to create an administrator-level account without authentication when a site exposes a public ACFE frontend form configured with a Create User action that maps a role field. The issue is caused by a validation bypass that can suppress role and capability checks.

CVE Details

  • CVE ID: CVE-2026-8809
  • Affected component: Advanced Custom Fields: Extended plugin for WordPress
  • Affected versions: All versions up to and including 0.9.2.5
  • Published: May 28, 2026 11:16:44 PM
  • Last modified: May 29, 2026 2:40:08 AM
  • CVSS v3.1 Base Score: 9.8 (CRITICAL)
  • CVSS v3.1 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  • Authentication / privileges / user interaction: No authentication required, privileges required: NONE, user interaction: NONE
  • Primary impact: Confidentiality: HIGH; Integrity: HIGH; Availability: HIGH
  • Weakness (CWE): CWE-269

Technical Details

The vulnerability exists because the plugin function after_validate_save_post() unconditionally trusts the attacker-controlled _acf_post_id POST parameter to select a cleanup branch. There is no authentication or integrity verification of that parameter. The cleanup branch silently discards validation errors that are not prefixed with acfe:, allowing suppression of important validation failures.

Two specific validation checks noted in the analysis can be suppressed: the role allow-list validation error added by acfe_field_user_roles::validate_front_value(), and the administrator-role capability guard error added by acfe_module_form_action_user::validate_action(). When those checks are suppressed, wp_insert_user() may be called with an attacker-supplied administrator role argument, resulting in creation of a new administrator-level user account.

Exploitation requires the target site to expose a public ACFE frontend form that includes a Create User action and maps a role field. The issue is a validation bypass rather than a flaw in WordPress core functions.

How This Could Impact Your Website

Consider a typical small site where the site owner manages users, an internal staff editor creates content, and an external contractor or contributor helps with front-end form submissions. If the site has a public ACFE frontend form configured to create users and map roles, an unauthenticated attacker could submit crafted form data that suppresses role and capability validations and results in a new administrator account.

Practical consequences include exposure of internal user email addresses via abuse of user management workflows and an increased risk of targeted phishing or social engineering against staff because attacker accounts could be used to access internal pages or send messages. The impact is tied to privilege escalation and should not be interpreted as automatic full-site compromise, but it does materially increase risk to site integrity and confidential data.

If youre unsure whether your site is affected or how to assess your current user roles and plugins, it may be worth having a professional review your setup.

Recommended Actions

  • Update the affected plugin as soon as a patched version is available.
  • Review and reduce unnecessary user roles, especially contributor-level mappings on public forms.
  • Enforce strong passwords and two-factor authentication for editors and administrators.
  • Remove unused or unmaintained plugins and disable public user-creation forms if not required.
  • Monitor site activity and logs for unusual behavior, including unexpected user creations and role changes.

If youd like help reviewing your plugins, user roles, or overall WordPress security posture, our team at Freshy is happy to help.

References

Nick Paliughihttps://freshysites.com/team/nick-paliughi/
Nick was born in California and now resides in Lake Worth, FL. He has 10 years of experience building and maintaining sites in WordPress, which he is excited to put to use at Freshy. Prior to starting at Freshy in 2022 his focus was on WordPress security & malware removal. When he’s not tending to your website, Nick is installing exhibitions at art galleries and museums in Palm Beach County, and if he’s lucky surfing at the Lake Worth pier.

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