Summary

A privilege/authorization omission exists in the Invoct – PDF Invoices & Billing for WooCommerce plugin (versions up to and including 1.6). Authenticated users with a Subscriber-level account can access functionality that should be restricted, potentially revealing invoices, billing details, customer emails, or other order-related information. Exploitation requires an authenticated account; there is no indication this vulnerability grants remote code execution or direct site takeover.

Why broken access control matters — even for “low” severity findings

Broken access control means the server-side code fails to verify whether the caller is permitted to perform the requested action. In WordPress this typically manifests as missing capability checks (current_user_can()), absent permission callbacks on REST endpoints, missing nonce validation, or unsecured AJAX handlers.

Practical impacts:

• Data exposure: invoices, customer contact details, or order metadata may be retrievable by low-privileged accounts.
• Compliance risk: exposed personal data can create GDPR/PDPO/CCPA obligations for merchants.
• Lateral abuse: compromised Subscriber accounts can be used to harvest data for targeted phishing or fraud.
• Reconnaissance: exposed internal endpoints reveal implementation details and order IDs that aid follow-up attacks.

Although the CVSS score is low, commerce websites should treat such exposure seriously because the value of invoice and customer data to attackers is high.

What the vulnerability allows (concise)

• The plugin exposes endpoints (likely AJAX/REST or admin-facing handlers) that do not perform sufficient authorization checks.
• Subscriber-level accounts can call those endpoints to retrieve invoice/billing data for orders they should not be able to see.
• Exploitation requires an authenticated account; anonymous users cannot exploit the issue without registering.

The correct long-term fix is server-side authorization on all sensitive endpoints. In the interim, use multi-layer mitigations.

How an attacker might exploit this

1. Create or use an existing Subscriber account on the store.
2. Discover the unprotected endpoint via normal UI flows or by inspecting JavaScript network calls.
3. Call the endpoint while manipulating parameters (order IDs, invoice IDs) to retrieve other customers’ data.
4. Exfiltrate the returned payloads (PDFs, JSON with emails/orders).

This class of exploit is straightforward: it requires an account and knowledge of where to call the endpoint.

How to check whether your site is affected

1. Check plugin version: WP Admin → Plugins — confirm whether Invoct is installed and version is ≤ 1.6.
2. Test as a Subscriber (use staging):
   • Create a test user with the Subscriber role and log in as that user.
   • Attempt to access pages or features that should be admin-only (viewing invoices for other orders, exporting billing data).
   • Monitor browser DevTools Network tab for AJAX/REST calls and try repeating those calls directly (e.g., curl) while authenticated as the Subscriber.
3. Inspect logs:
   • Search server and application logs for requests to plugin-specific endpoints or suspicious parameter combinations that return invoice data.
4. Automated scanning: Run an SCA/vulnerability scanner that tracks CVE-2026-1748 in staging to detect affected instances.

Always test in staging and avoid exercising production customer data without permission.

Immediate mitigation steps (fastest to implement)

If you cannot immediately update the plugin, apply these mitigations in order of speed and impact:

1. Deactivate the plugin if invoice functionality is not required for core operations. This fully removes the vulnerability.
2. Limit Subscriber capabilities — reduce what Subscriber accounts can access until a patch is available (see the virtual patch below).
3. Server-level blocking — block or limit access to plugin files/endpoints at the web server or WAF unless the session is from a high-capability user.
4. Protect invoice files — if PDFs are stored publicly, move them outside the webroot or restrict direct access with .htaccess rules (or serve via a PHP access gate that enforces current_user_can()).
5. Monitoring and alerting — create log alerts for repeated invoice downloads or admin-ajax.php calls with invoice-related action parameters.

Temporary WordPress-level virtual patch (mu-plugin)

Place the following as a mu-plugin (wp-content/mu-plugins/invoct-auth-guard.php) so it loads before the Invoct plugin. Adjust action/route names to match the plugin implementation.

<?php
/*
Plugin Name: Invoct Auth Guard (temporary virtual patch)
Description: Authorization wrapper that blocks non-privileged users from accessing Invoct endpoints.
Author: Hong Kong Security Team
*/

add_action('init', function() {
    // Protect REST endpoints by strengthening permission callbacks for routes that mention 'invoct' or 'invoice'
    add_filter('rest_endpoints', function($endpoints) {
        foreach ($endpoints as $route => $handlers) {
            if (strpos($route, '/invoct') !== false || strpos($route, '/invoice') !== false) {
                foreach ($handlers as $idx => $handler) {
                    if (is_array($handler) && isset($handler['permission_callback'])) {
                        $orig = $handler['permission_callback'];
                        $handlers[$idx]['permission_callback'] = function($request) use ($orig) {
                            if (is_callable($orig) && !$orig($request)) {
                                return false;
                            }
                            // Allow only shop managers / admins by default
                            return current_user_can('manage_woocommerce') || current_user_can('manage_options');
                        };
                    } else {
                        $handlers[$idx]['permission_callback'] = function($request) {
                            return current_user_can('manage_woocommerce') || current_user_can('manage_options');
                        };
                    }
                }
                $endpoints[$route] = $handlers;
            }
        }
        return $endpoints;
    }, 99);

    // Protect example AJAX action 'invoct_get_invoice'
    add_action('wp_ajax_invoct_get_invoice', function() {
        if (!current_user_can('manage_woocommerce') && !current_user_can('manage_options')) {
            wp_die('Unauthorized', 403);
        }
        // If authorized, allow normal processing to continue
    }, 1);
});

Notes:

• The snippet is conservative: it restricts access to shop managers and admins. Adjust capabilities to match your operational needs.
• Search the plugin source to identify exact AJAX action names or REST routes and update the mu-plugin accordingly.
• Use staging to validate before deploying to production.

ModSecurity / WAF rule examples (conceptual)

Below are example rules you can adapt to your WAF. Test in detection mode first to avoid blocking legitimate traffic.

1) Detect access to plugin folder paths

SecRule REQUEST_URI "@rx /wp-content/plugins/(invoct|pdf-invoice|pdf-invoices)/" \
    "id:1000001,phase:1,pass,log,tag:invoct,ctl:ruleEngine=DetectionOnly,msg:'Invoct plugin path accessed'"

2) Block plugin path for non-privileged users (example)

SecRule REQUEST_URI "@rx /wp-content/plugins/(invoct|pdf-invoice|pdf-invoices)/" \
    "id:1000002,phase:2,deny,log,status:403,msg:'Blocked plugin path for non-privileged users',chain"
    SecRule &REQUEST_HEADERS:Cookie "@gt 0" "chain"
    SecRule REQUEST_HEADERS:Cookie "!@contains current_user" "t:none"

3) Block admin-ajax calls with suspicious actions from unauthenticated/low-privilege requests

SecRule REQUEST_URI "@beginsWith /wp-admin/admin-ajax.php" "id:1000010,phase:2,pass,nolog,chain"
    SecRule ARGS:action "@rx invoct|invoice|billing|get_invoice" "t:none,chain"
    SecRule REQUEST_HEADERS:Cookie "!@contains wp_logged_in" "t:none"
    SecAction "deny,log,status:403,msg:'Blocked invoice AJAX call from unauthenticated or non-priv user' "

4) Rate-limit suspicious extraction

Create rules to limit invoice downloads per user/session/IP to reduce mass exfiltration (e.g., 10 per hour per account). Exact syntax depends on your WAF.

Implementation notes: adapt these to your environment and test thoroughly. If you use a managed WAF service, ask them to add virtual patching that denies invoice APIs to non-privileged accounts.

Detecting exploitation — indicators of compromise

Search for these patterns in logs:

• Multiple admin-ajax.php requests with invoice-related action parameters originating from legitimate user accounts.
• Subscriber accounts accessing endpoints or pages normally reserved for store staff.
• High-volume PDF downloads of invoice files from many Subscriber accounts or IP addresses.
• REST requests returning payloads with order/customer details when called by low-privileged sessions.
• Newly created users followed quickly by invoice API calls.

Logging recommendations:

• Enable request logging for admin-ajax.php and REST endpoints (including POST bodies where permitted).
• Retain logs for at least 90 days if customer data could be exposed.
• Create alerts for thresholds (e.g., X invoice downloads per hour by a single account).

Long-term remediation & secure design checklist

1. Update the plugin once the vendor releases a patch. The vendor must add server-side authorization checks and proper permission callbacks.
2. Principle of least privilege: Re-evaluate registration flows; consider disabling automatic Subscriber registration or enforcing stronger verification (CAPTCHA, email confirmation).
3. Developer checklist:
   • Validate capabilities (current_user_can) on every action that returns sensitive data.
   • Use WP nonces for forms/AJAX where relevant and validate server-side.
   • Define proper permission_callback functions for REST routes.
   • Never rely solely on client-side checks.
   • Rate-limit and log sensitive actions.
4. Layered defence: Harden WordPress (disable file editing, limit XML-RPC if unused), retain WAF protections, and perform regular scans for exposed endpoints.
5. Periodic audits: Schedule security code reviews for plugins that handle commerce data.

Practical .htaccess example for protecting stored PDFs

If invoices are stored under a public folder (example: wp-content/uploads/invoct-invoices), prefer moving files outside the webroot and serving via PHP with a permission check. If that is not possible, a simple conceptual .htaccess approach:

# Deny direct access to invoice files
<FilesMatch "\.(pdf|zip)$">
    Require all denied
</FilesMatch>

# Note: The above denies direct file access. A robust alternative is to store files outside webroot and serve via a PHP script that checks current_user_can() for the requested invoice.

If you suspect a compromise

1. Confirm whether the vulnerable plugin is installed and version ≤ 1.6.
2. If confirmed:
   • Deactivate the plugin or apply the mu-plugin virtual patch and WAF rules.
   • Enable high-fidelity logging for admin-ajax and REST endpoints.
   • Rotate credentials for admin/shop-manager accounts and force password resets for potentially affected users.
   • Revoke persistent API keys that may be in use.
3. Collect forensic snapshots of logs and filesystem prior to remediation actions for incident response purposes.
4. If data exposure is confirmed, follow applicable disclosure/regulatory procedures (consult legal/compliance).
5. When a vendor patch is available, test in staging and apply to production promptly.

FAQ (short)

Does this vulnerability allow site takeover?

No — it is primarily an information exposure through missing authorization checks. It does not appear to allow code execution or privilege escalation by itself, though exposed data can be used for social engineering.

Can anonymous visitors exploit it?

No. Exploitation requires an authenticated account (Subscriber or higher). Anonymous visitors would need to register to gain a Subscriber account.

Should I remove the plugin immediately?

If the plugin is not essential, deactivating it is the fastest and most reliable mitigation. If you must keep it, apply the virtual patch and WAF rules until an official fix is released.

Will my host protect me?

Many hosts can deploy WAF rules or server-level blocks. If your host offers such services, request a virtual patch that denies invoice endpoints to non-privileged accounts and rate-limits downloads.

Final notes — from a Hong Kong security practitioner

Broken access control is a server-side logic error that must be addressed in application code. Until a vendor patch is available, reduce risk by combining quick fixes (deactivate plugin or apply a mu-plugin), server/WAF rules, and active monitoring. Document and retain logs for incident response and compliance.

If you need implementation assistance, engage a qualified security professional or reach out to your hosting provider to apply WAF/ModSecurity rules and review the mu-plugin approach. Prioritise staged testing to avoid unintended service disruptions.

Security in commerce systems is layered and operational. Apply these mitigations quickly and monitor closely until the plugin is patched.