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CVE-2026-87796 – Unauthenticated Arbitrary File Upload / RCE – Multi Uploader for Gravity Forms ≤ 1.

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Summary

CVE-2026-87796 is a critical unauthenticated arbitrary file upload vulnerability in the "Multi Uploader for Gravity Forms" WordPress plugin (developed by sh1zen), affecting all versions up to and including 1.1.9. The flaw stems from insufficient file type validation in the plugin’s chunked upload handling, and can allow an unauthenticated attacker to upload arbitrary files — including executable PHP code — to the affected server. The issue is rated CRITICAL with a CVSS v3.1 base score of 9.8.

Technical details

  • Root cause: The plugin’s chunked file upload logic (implemented around the move_file handling in the plugin’s uploader classes) fails to properly validate the type/extension of files being reassembled from uploaded chunks before writing them to disk.
  • Trigger conditions: An attacker sends crafted chunked upload requests to the plugin’s upload endpoint on a WordPress site running the vulnerable plugin; no authentication or user interaction is required.
  • Attack vector: Network — the endpoint is reachable by any unauthenticated visitor to a site with a form using the Multi Uploader for Gravity Forms field.
  • Impact: Successful exploitation allows an attacker to place arbitrary files (e.g., a PHP web shell) on the server’s file system, which can lead to full remote code execution, complete compromise of the WordPress site, and downstream compromise of the hosting environment.
  • Weakness class: CWE-434 (Unrestricted Upload of File with Dangerous Type).

Affected software

  • Multi Uploader for Gravity Forms (WordPress plugin, developer: sh1zen) — all versions up to and including 1.1.9

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: No patched version has been publicly released for this issue as of this writing; version 1.1.9 remains the latest released version and is vulnerable. The plugin has also been temporarily removed from the WordPress.org plugin directory (closed as of September 11, 2026) pending review, meaning it is not currently available for new installs or updates through the official repository.
  • If no patch is available:
    • Deactivate and remove the "Multi Uploader for Gravity Forms" plugin from affected WordPress sites until an official fix is released.
    • If the plugin must remain active, restrict or block public access to its upload endpoints at the web server or WAF layer.
    • Audit the wp-content/uploads directory and any plugin-specific upload paths for unexpected or executable files (e.g., .php, .phtml, .phar) placed outside of expected media types.
    • Monitor web server and WordPress logs for unusual POST requests to chunked-upload-related endpoints.
    • Restrict execution of scripts within uploads directories via server configuration (e.g., disabling PHP execution in wp-content/uploads).

References

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