Broken Access Control in Smart Forms (<= 2.6.99) — What WordPress Site Owners Must Do Now

Auteur : Expert en sécurité de Hong Kong

Publié : 13 févr. 2026

Gravité : Low (CVSS 4.3) — Classification: Broken Access Control

Versions affectées : Smart Forms plugin ≤ 2.6.99

CVE : CVE-2026-2022

Résumé : ce qui s'est passé et pourquoi cela compte

• Smart Forms exposes campaign-related data through endpoints (AJAX/REST) that lack adequate authorization checks.
• Authenticated users with the Subscriber role can access campaign data intended for administrators or users with higher privileges.
• This is a classic Broken Access Control issue (OWASP A1) and is tracked as CVE‑2026‑2022.
• The primary impact is information disclosure. Depending on how the plugin stores campaign data, leaked items could include email templates, metadata, recipient lists, tracking tokens or links. While rated low for general impact, such information can be valuable for targeted phishing or intelligence gathering.

Context from a Hong Kong security practitioner’s perspective

In Hong Kong we often see sites that allow open Subscriber registrations for community, retail or marketing workflows. Wherever open registration exists, access-control lapses like this rapidly increase risk. The defensive posture should be pragmatic and layered: detect, reduce exposure, and patch. Below I present a practical, no-nonsense walkthrough that you can use immediately.

Technical root cause (plain language)

This is not an authentication bypass. The endpoints typically require the user to be logged in. The missing piece is authorization: the server fails to verify whether the authenticated user is permitted to view campaign data.

Common developer mistakes that lead to this class of bug:

• Registering admin AJAX actions without capability checks in the handler.
• Registering REST API routes without a proper permission_callback dans register_rest_route.
• Returning sensitive data based solely on an authenticated session (treating authenticated == trusted).
• Relying on client-side checks (hiding UI) while leaving server endpoints unrestricted.

Design principle: never trust the client; always enforce authorization server-side.

High-level attack scenario

1. Attacker creates or uses a Subscriber account on a site that allows such registrations.
2. Attacker authenticates and sends crafted AJAX or REST requests to plugin endpoints that expose campaign data.
3. The server responds because it only checked for authentication, not whether the caller has the right capability.
4. Attacker exfiltrates campaign data: email subject lines, template bodies, recipient lists, tokens, tracking links, etc.
5. Exfiltrated data may be used for phishing, impersonation, or as reconnaissance for further attacks.

This attack requires a logged-in Subscriber; it is not an anonymous remote exploit. Sites with open registration are therefore at higher risk.

What to do immediately — step-by-step checklist

Follow these steps in order. Take action now if you run Smart Forms ≤ 2.6.99.

1. Inventory and exposure assessment
   • Confirm Smart Forms is installed and active, and note the plugin version (WP‑Admin → Plugins or WP‑CLI).
   • Check whether your site allows user registration and what default role is assigned (WP‑Admin → Settings → General → New User Default Role).
2. Reduce attack surface (temporary)
   • If possible, deactivate the plugin until a fix is available (WP‑Admin → Plugins → Deactivate Smart Forms).
   • If you cannot deactivate it, restrict access to the plugin endpoints by adding WAF / reverse-proxy rules, an MU-plugin, or webserver rules (.htaccess/nginx).
3. Harden user registrations
   • Disable public registration where not required, or set the default role to a role with no content access.
   • Consider manual approval for new accounts or additional verification steps.
4. Faire tourner les secrets
   • If you discover leaked tokens, API keys or tracking credentials, rotate them immediately.
5. Surveillez les journaux
   • Search web and application logs for suspicious activity (patterns below).
6. Apply temporary protections
   • Deploy virtual patches via your WAF/reverse-proxy or add MU-plugin restrictions to block Subscriber access to campaign endpoints until the plugin is updated.
7. Apply official fixes when available
   • When the plugin author releases an update, apply it promptly and then remove temporary mitigations after verifying the fix.

Detection: how to tell if someone tried to exploit this

Look for the following indicators in server and WordPress logs:

• Unusual or high-volume admin-ajax.php or REST API requests from authenticated Subscriber accounts.
• Requests with action names or endpoints related to campaign, mailing, forms, sms.
• REST paths such as /wp-json/*/campaigns, /wp-json/*/mailing*, /wp-json/*/forms/*/campaigns.
• Subscriber accounts producing data responses containing campaign fields.
• Enumeration-like request patterns (e.g., repeated ?id= ou ?campaign_id= probes).
• JSON responses containing keywords: “campaign”, “template”, “subject”, “recipient”, “emails”, “token”, “tracking”.

Shell search examples:

# Search access logs for admin-ajax hits with "campaign" in query
grep "admin-ajax.php" /var/log/apache2/access.log | grep -i campaign

# Search REST requests
grep "wp-json" /var/log/nginx/access.log | grep -i campaign

Vérifiez wp-content/debug.log for plugin notices that may reveal endpoint names.

Safe, non-exploitative proof-of-concept (sanitised)

For detection and testing only — do not use against systems you do not own.

GET /wp-json/plugin-namespace/v1/campaigns/123 HTTP/1.1
Host: example.com
Cookie: wordpress_logged_in_...
Accept: application/json

If this returns campaign details when performed with a Subscriber session, the endpoint is improperly authorised.

Quick temporary fixes (no plugin update required)

If you cannot immediately update the plugin, consider these mitigations:

1. Block endpoints via WAF / reverse-proxy (virtual patch)

Use your edge protection or reverse-proxy to block or challenge requests matching the plugin’s REST namespace or AJAX patterns. Example rule concepts:

• If request path contains /wp-json/smartforms ou /wp-json/sf then block or challenge.
• Si admin-ajax.php is called with action values associated with campaigns and the user is a Subscriber, block the request.
• Prefer “challenge” (CAPTCHA) and whitelisting trusted IPs if third-party integrations use the same namespace.

2. Add an MU-plugin to enforce server-side checks

Create a must-use plugin that intercepts REST and AJAX requests and returns 403 for Subscribers attempting to access campaign resources. This is a temporary, defensive guard.

<?php
// File: wp-content/mu-plugins/deny-subscriber-campaigns.php
add_action('init', function() {
    // REST request detection
    if (defined('REST_REQUEST') && REST_REQUEST) {
        $uri = $_SERVER['REQUEST_URI'];
        if (strpos($uri, '/wp-json/smartforms') !== false || strpos($uri, '/wp-json/sf') !== false) {
            if (is_user_logged_in() && current_user_can('subscriber')) {
                wp_die('Forbidden', 403);
            }
        }
    }

    // admin-ajax detection
    if (isset($_SERVER['SCRIPT_NAME']) && basename($_SERVER['SCRIPT_NAME']) === 'admin-ajax.php') {
        $action = $_REQUEST['action'] ?? '';
        // adjust action names to match plugin (use logs to confirm)
        $campaign_actions = ['get_campaign', 'get_campaigns', 'smartforms_get_campaign'];
        if (in_array($action, $campaign_actions, true)) {
            if (is_user_logged_in() && current_user_can('subscriber')) {
                wp_die('Forbidden', 403);
            }
        }
    }
}, 1);

Remarques :

• Adjust action names and REST paths to match what your logs show.
• This is a stop-gap until an official plugin update is applied.

3. Webserver rules (.htaccess / nginx)

Restrict traffic to known REST namespaces or admin-ajax patterns by IP, or deny access entirely for unknown sources. Be careful to avoid breaking legitimate integrations.

Developer patch guidance (what the plugin author should do)

If you maintain the plugin, apply these server-side fixes:

1. Appliquez des vérifications de capacité

   AJAX handlers must verify capabilities, not just authentication:

   add_action('wp_ajax_get_campaign', 'sf_get_campaign_callback');
   function sf_get_campaign_callback() {
       if (! current_user_can('manage_options')) { // or a plugin-specific capability
           wp_send_json_error('Not allowed', 403);
       }
       // proceed...
   }
   

2. Use register_rest_route with permission_callback

   register_rest_route('smartforms/v1', '/campaigns/(?P<id>\d+)', array(
       'methods' => 'GET',
       'callback' => 'sf_rest_get_campaign',
       'permission_callback' => function() {
           return current_user_can('manage_options');
       }
   ));
   

3. Use nonces for state-changing operations

   Validate nonces server-side with wp_verify_nonce() ou check_ajax_referer().

4. Return least-privilege data

   Only include fields necessary for the caller. Sensitive fields should be returned only to authorised roles.

5. Journalisation et audit

   Log access to sensitive endpoints with account identifiers for incident response.

6. Tests automatisés

   Add tests to ensure low-privilege users cannot access restricted endpoints.

7. Document capability mappings

   Provide clear documentation so site owners can configure who can access campaign data.

Virtual patch examples (WAF / edge rule templates)

Below are practical rule templates you can implement in your WAF or reverse-proxy. Test in monitor mode first.

1. Block REST namespace
   • Match: Request Path contains /wp-json/smartforms ou /wp-json/sf
   • Condition: Request Method is GET (or include POST if relevant)
   • Action: Block (403) or Challenge (CAPTCHA)
2. Block admin-ajax campaign actions
   • Match: Request Path equals */admin-ajax.php
   • Condition: Query parameter action is in the campaign-action list
   • Condition: Request is authenticated and appears to be a Subscriber (cookie analysis)
   • Action : Bloquer
3. Faire respecter la présence de nonce
   • Correspondre : admin-ajax.php with campaign action
   • Condition: Missing X-WP-Nonce or invalid nonce header
   • Action: Challenge or Block
4. Rate-limit Subscriber access
   • Match: Subscriber-authenticated requests to admin-ajax or REST path
   • Condition: Requests per minute > threshold (example: 10/min)
   • Action: Throttle or temporary block
5. Block enumeration patterns
   • Match: Repeated requests containing ?id=\d+ ou campaign_id=\d+
   • Action: Block or blacklist IP temporarily

These virtual patches provide immediate mitigation across many sites without changing plugin code.

Incident response: if you suspect data was exfiltrated

If logs indicate suspicious access to campaign endpoints, follow these steps quickly:

1. Block or disable offending accounts and rotate any exposed tokens.
2. Reset administrator passwords and any accounts used for pivoting.
3. Revoke and rotate API keys that could be embedded in campaigns or templates.
4. Preserve logs and take a snapshot of files and database for forensic analysis.
5. Run full malware and integrity scans; look for unexpected admin users, scheduled tasks, or unknown uploads.
6. Communicate with stakeholders and follow local breach notification requirements if PII is involved.
7. If necessary, engage a reputable incident response provider or security consultant to assist.

Hardening checklist (longer-term)

• Enforce MFA for all administrative accounts.
• Limit plugin installation/activation to a small set of trusted administrators.
• Regularly scan for vulnerable plugins and apply verified updates promptly.
• Perform role audits: remove unused accounts and enforce least privilege.
• Monitor and alert on suspicious endpoints and anomalous Subscriber behaviour.
• Keep WAF/edge rules and virtual patches up to date.
• Encourage plugin authors to adopt secure-by-default patterns (permission callbacks, capability checks, nonces).

How site owners can test whether their site is vulnerable (safe approach)

1. Create a Subscriber test account and log in.
2. Use browser developer tools to observe Smart Forms network requests (admin-ajax or REST calls).
3. From the Subscriber session, attempt read-only GET to identified endpoints (use console or curl against a staging instance).
4. If the endpoint returns campaign payloads while authenticated as a Subscriber, it is improperly authorised.

Always test on staging or with accounts you control.

Practical examples: secure REST and AJAX handlers for developers

REST endpoint (secure)

add_action('rest_api_init', function () {
    register_rest_route('smartforms/v1', '/campaigns/(?P<id>\d+)', array(
        'methods' => 'GET',
        'callback' => 'smartforms_rest_get_campaign',
        'permission_callback' => function () {
            // Only administrators or users with a custom capability can access full campaign data
            return current_user_can('manage_options') || current_user_can('smartforms_view_campaigns');
        }
    ));
});

AJAX handler (secure)

add_action('wp_ajax_get_campaign', 'smartforms_get_campaign_ajax');
function smartforms_get_campaign_ajax() {
    // Check capabilities
    if (! current_user_can('manage_options') && ! current_user_can('smartforms_view_campaigns')) {
        wp_send_json_error('Unauthorized', 403);
    }
    // Validate nonce
    check_ajax_referer('smartforms_nonce_action', 'security');

    // Return limited data
    $id = intval($_REQUEST['id']);
    $campaign = get_smartforms_campaign($id);
    wp_send_json_success(array(
        'id' => $campaign->id,
        'title' => sanitize_text_field($campaign->title),
        // hide sensitive fields unless admin
    ));
}

Key points for developers: verify capabilities, validate nonces, and sanitize outputs. Tests should assert that low-privilege users cannot access restricted fields.

Why this class of vulnerability matters beyond this plugin

Broken access control is a frequent and impactful web weakness. Developers often assume UI restrictions are sufficient; in reality only server-side checks enforce true access control. Even low-severity leaks can provide reconnaissance useful for phishing, impersonation, or further exploitation.

Closing guidance — immediate priorities

• If Smart Forms (≤2.6.99) is active on your site, assume it may be vulnerable. Deactivate it or apply mitigations (WAF rules, MU-plugin, registration hardening) immediately.
• Audit logs for suspicious Subscriber activity and follow the incident response steps if you find evidence of access to campaign endpoints.
• Developers and plugin vendors: audit all endpoints for missing permission checks, add permission_callback for REST routes, and require nonces for AJAX handlers.
• If you need assistance, hire a reputable security consultant or incident response provider to apply temporary virtual patches and perform a forensic review.

Protecting WordPress requires layered defenses: strict server-side authorization, careful role management, prompt updates, and edge protections to mitigate zero-days or delayed fixes. Follow the steps above to reduce exposure from this Smart Forms issue and strengthen your site for the future.