What is CVE-2026-65499?

CVE-2026-65499 is a missing authorization vulnerability in the PeproDev Ultimate Invoice plugin for WordPress, affecting versions up to and including 2.2.6. It allows unauthenticated attackers to perform unauthorized actions due to a missing capability check on a specific function. The vulnerability has a CVSS score of 5.3 (Medium) and is classified under CWE-862.

How does this vulnerability work?

The plugin registers an AJAX action or similar callback without verifying that the requesting user has the required capability. Because the endpoint is accessible to unauthenticated users (often via the nopriv hook), an attacker can send a crafted HTTP request to admin-ajax.php with the action parameter set to the vulnerable hook name. The lack of a nonce or capability check allows the request to trigger the unauthorized action.

Who is affected by this vulnerability?

Any WordPress site running the PeproDev Ultimate Invoice plugin version 2.2.6 or earlier is affected. Since the vulnerability can be exploited without authentication, all sites with the vulnerable plugin installed are at risk, regardless of user roles. Administrators should check their plugin version and update or remove it if vulnerable.

How can I check if my site is vulnerable?

Check the installed version of the PeproDev Ultimate Invoice plugin in the WordPress admin dashboard under Plugins. If the version is 2.2.6 or lower, the site is vulnerable. Additionally, you can review the plugin’s code for any AJAX actions registered with ‘wp_ajax_nopriv_’ without a capability check, but this requires technical expertise. For a quick check, look for any recent security advisories or updates from the plugin developer.

What is the practical risk of this vulnerability?

The CVSS vector indicates a low integrity impact, meaning an attacker can modify data but cannot access confidential information or cause denial of service. In practice, an attacker could alter invoice data, change plugin settings, or trigger other unauthorized actions that affect the integrity of accounting records. This could lead to financial discrepancies or loss of trust in the invoicing system.

How does the proof of concept (PoC) demonstrate the issue?

The provided PoC sends a POST request to the WordPress admin-ajax.php endpoint with an action parameter set to a placeholder for the vulnerable hook. It includes no authentication tokens or nonces, demonstrating that the endpoint is accessible without login. The PoC is metadata-based, so the exact action name must be adjusted based on the actual plugin code, but it illustrates how an unauthenticated attacker could trigger the vulnerable function.

What is the root cause of this vulnerability?

The root cause is a missing capability check in a function that handles AJAX requests or similar callbacks. The plugin fails to use current_user_can() or a similar authorization check to verify that the user has the necessary permissions. This is a common issue in WordPress plugins where administrative functions are exposed without proper access control.

How can I fix or mitigate this vulnerability?

The immediate mitigation is to disable or uninstall the plugin until a patched version is released. If you cannot remove it, you can apply a temporary workaround by adding a capability check to the vulnerable function via a code snippet, but this requires custom development. The developer should release an update that adds proper authorization checks, such as current_user_can() and nonce verification.

Is there a patched version available?

As of the disclosure date, no patched version has been released. The vulnerability affects versions up to and including 2.2.6, and the developer has not yet provided an update. Users should monitor the plugin’s changelog for a security fix and consider alternative invoicing plugins if an update is not forthcoming.

What actions can an attacker perform with this vulnerability?

An attacker could perform any action that the vulnerable function is designed to do, such as creating or updating invoices, modifying plugin settings, or triggering email notifications. The exact impact depends on the function’s purpose. Since the CVSS vector shows low integrity impact, the attacker can alter data but cannot access sensitive information or cause a full system compromise.

Does this vulnerability require authentication?

No, the vulnerability can be exploited by unauthenticated attackers. The missing capability check means that no user account or login is required. The attacker only needs to send a crafted HTTP request to the vulnerable endpoint, making it easy to exploit remotely.

How does the CVSS score of 5.3 translate to real-world severity?

A CVSS score of 5.3 is considered Medium severity. It indicates that the vulnerability is moderately serious, with a low impact on integrity but no impact on confidentiality or availability. In practical terms, it means the vulnerability is exploitable without authentication and could cause unauthorized data modification, but it does not lead to data theft or service disruption. Administrators should prioritize fixing it, but it is not as critical as high-severity issues.

Published : August 11, 2026

CVE-2026-65499: PeproDev Ultimate Invoice <= 2.2.6 Missing Authorization PoC, Patch Analysis & Rule

CVE ID CVE-2026-65499

Plugin pepro-ultimate-invoice

Severity Medium (CVSS 5.3)

CWE 862

Vulnerable Version 2.2.6

Patched Version —

Disclosed July 22, 2026

Analysis Overview

Atomic Edge analysis of CVE-2026-65499 (metadata-based):
This vulnerability affects the PeproDev Ultimate Invoice plugin for WordPress, version 2.2.6 and earlier. The plugin fails to enforce a capability check on a specific function, allowing unauthenticated users to perform an unauthorized action. The CVSS score is 5.3 (Medium), with the vector AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N, indicating low integrity impact without any confidentiality or availability impact.

The root cause, based on the CWE-862 (Missing Authorization) classification and the vulnerability description, is that the plugin registers an AJAX action or a similar callback (likely via add_action(‘wp_ajax_nopriv_…’) or a REST API route) without verifying that the requesting user has the required capability (e.g., edit_posts, manage_options, or a custom invoice capability). The description explicitly states that there is a missing capability check, which is confirmed from the metadata. Atomic Edge analysis infers that the vulnerable function is likely an AJAX handler, because WordPress plugins commonly expose administrative features through admin-ajax.php, and the nopriv prefix would make the endpoint accessible to unauthenticated users. No source code is available, so the exact function name and parameter structure are not confirmed.

Exploitation requires no authentication. An attacker sends a crafted HTTP request to /wp-admin/admin-ajax.php with the action parameter set to the vulnerable hook name. Because the plugin does not verify nonces or capabilities, the request does not need a valid nonce. The attacker would include the parameters the vulnerable function expects to trigger the unauthorized action. Atomic Edge research suggests that the action name likely follows a pattern such as pepro_ultimate_invoice_* or a similar slug-derived prefix, based on WordPress conventions, but the exact action name remains unconfirmed from metadata alone.

Remediation requires adding a capability check to the vulnerable function. The developer should verify that the current user has the appropriate permission before executing the action, for example by using current_user_can(). Additionally, the plugin should verify a nonce if the action is invoked from the WordPress admin area. If the function is intended to be public, the developer must implement proper access control to ensure it only performs actions that unauthenticated users are allowed to do. Since no patched version is available, users should disable or uninstall the plugin until an update is released.

The impact is limited to unauthorized actions that modify data or trigger plugin-specific operations, such as creating or updating invoices, altering plugin settings, or sending emails. The CVSS vector indicates a low integrity impact, meaning an attacker can modify data without affecting confidentiality or availability. There is no direct privilege escalation or data disclosure. However, if the vulnerable function can alter critical plugin data, the integrity impact could affect the reliability of the accounting or invoicing records.

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 (metadata-based)
// CVE-2026-65499 - PeproDev Ultimate Invoice <= 2.2.6 - Missing Authorization

// This PoC demonstrates an unauthenticated request to the vulnerable AJAX action.
// The exact action name is not confirmed from metadata; adjust the ACTION constant
// based on the actual plugin code once available.

$target_url = 'http://example.com/wp-admin/admin-ajax.php';
$action = 'pepro_ultimate_invoice_some_action'; // Replace with actual vulnerable action

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $target_url);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, [
    'action' => $action,
    // Include any additional parameters required by the vulnerable function
    // 'invoice_id' => '1',
    // 'status' => 'cancelled',
]);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, false);
curl_setopt($ch, CURLOPT_HTTPHEADER, [
    'Content-Type: application/x-www-form-urlencoded',
]);

$response = curl_exec($ch);
$http_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
curl_close($ch);

echo "HTTP Status: " . $http_code . "n";
echo "Response: " . $response . "n";

// If the action is a REST API endpoint, use something like:
// $target_url = 'http://example.com/wp-json/pepro-invoice/v1/endpoint';
// and send a GET or POST request as appropriate.

Frequently Asked Questions

What is CVE-2026-65499?
Vulnerability overview
CVE-2026-65499 is a missing authorization vulnerability in the PeproDev Ultimate Invoice plugin for WordPress, affecting versions up to and including 2.2.6. It allows unauthenticated attackers to perform unauthorized actions due to a missing capability check on a specific function. The vulnerability has a CVSS score of 5.3 (Medium) and is classified under CWE-862.
How does this vulnerability work?
Technical mechanism
The plugin registers an AJAX action or similar callback without verifying that the requesting user has the required capability. Because the endpoint is accessible to unauthenticated users (often via the nopriv hook), an attacker can send a crafted HTTP request to admin-ajax.php with the action parameter set to the vulnerable hook name. The lack of a nonce or capability check allows the request to trigger the unauthorized action.
Who is affected by this vulnerability?
Affected users
Any WordPress site running the PeproDev Ultimate Invoice plugin version 2.2.6 or earlier is affected. Since the vulnerability can be exploited without authentication, all sites with the vulnerable plugin installed are at risk, regardless of user roles. Administrators should check their plugin version and update or remove it if vulnerable.
How can I check if my site is vulnerable?
Detection steps
Check the installed version of the PeproDev Ultimate Invoice plugin in the WordPress admin dashboard under Plugins. If the version is 2.2.6 or lower, the site is vulnerable. Additionally, you can review the plugin’s code for any AJAX actions registered with ‘wp_ajax_nopriv_’ without a capability check, but this requires technical expertise. For a quick check, look for any recent security advisories or updates from the plugin developer.
What is the practical risk of this vulnerability?
Impact assessment
The CVSS vector indicates a low integrity impact, meaning an attacker can modify data but cannot access confidential information or cause denial of service. In practice, an attacker could alter invoice data, change plugin settings, or trigger other unauthorized actions that affect the integrity of accounting records. This could lead to financial discrepancies or loss of trust in the invoicing system.
How does the proof of concept (PoC) demonstrate the issue?
PoC explanation
The provided PoC sends a POST request to the WordPress admin-ajax.php endpoint with an action parameter set to a placeholder for the vulnerable hook. It includes no authentication tokens or nonces, demonstrating that the endpoint is accessible without login. The PoC is metadata-based, so the exact action name must be adjusted based on the actual plugin code, but it illustrates how an unauthenticated attacker could trigger the vulnerable function.
What is the root cause of this vulnerability?
Underlying issue
The root cause is a missing capability check in a function that handles AJAX requests or similar callbacks. The plugin fails to use current_user_can() or a similar authorization check to verify that the user has the necessary permissions. This is a common issue in WordPress plugins where administrative functions are exposed without proper access control.
How can I fix or mitigate this vulnerability?
Remediation steps
The immediate mitigation is to disable or uninstall the plugin until a patched version is released. If you cannot remove it, you can apply a temporary workaround by adding a capability check to the vulnerable function via a code snippet, but this requires custom development. The developer should release an update that adds proper authorization checks, such as current_user_can() and nonce verification.
Is there a patched version available?
Patch status
As of the disclosure date, no patched version has been released. The vulnerability affects versions up to and including 2.2.6, and the developer has not yet provided an update. Users should monitor the plugin’s changelog for a security fix and consider alternative invoicing plugins if an update is not forthcoming.
What actions can an attacker perform with this vulnerability?
Potential exploitation
An attacker could perform any action that the vulnerable function is designed to do, such as creating or updating invoices, modifying plugin settings, or triggering email notifications. The exact impact depends on the function’s purpose. Since the CVSS vector shows low integrity impact, the attacker can alter data but cannot access sensitive information or cause a full system compromise.
Does this vulnerability require authentication?
Authentication requirement
No, the vulnerability can be exploited by unauthenticated attackers. The missing capability check means that no user account or login is required. The attacker only needs to send a crafted HTTP request to the vulnerable endpoint, making it easy to exploit remotely.
How does the CVSS score of 5.3 translate to real-world severity?
Severity interpretation
A CVSS score of 5.3 is considered Medium severity. It indicates that the vulnerability is moderately serious, with a low impact on integrity but no impact on confidentiality or availability. In practical terms, it means the vulnerability is exploitable without authentication and could cause unauthorized data modification, but it does not lead to data theft or service disruption. Administrators should prioritize fixing it, but it is not as critical as high-severity issues.

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