CVE-2026-16587: 
WordPress vulnerability analysis and mitigation

CVE-2026-16587 is an authorization bypass vulnerability in the Advanced Form Integration — Connect Forms to 200+ Apps WordPress plugin, affecting all versions up to and including 2.6.0. The flaw allows authenticated attackers with subscriber-level access or higher to overwrite the site's stored MailUp OAuth tokens, redirecting form-submission data to an attacker-controlled account or disabling the integration entirely. It was published on July 28, 2026, with a patch released the same day. The vulnerability carries a CVSS v3.1 base score of 4.3 (Medium) (GitHub Advisory).

The root cause is a missing authorization check (CWE-862) in the plugin's MailUp integration code (platforms/mailup/mailup.php). The plugin hooks a sensitive token-update action to the admin_init WordPress hook without verifying whether the requesting user has the necessary privileges to modify OAuth credentials. Because admin_init fires for all logged-in users who visit any /wp-admin/ page — including the low-privilege /wp-admin/profile.php — any authenticated subscriber can trigger the vulnerable code path and overwrite the adfoin_mailup_keys option with attacker-controlled OAuth tokens. Relevant vulnerable code lines are documented at plugin revision 2.6.0 (lines 51, 98, 375, and 411 of mailup.php) (GitHub Advisory).

Successful exploitation allows an authenticated attacker to redirect all future MailUp-integrated form submissions (e.g., newsletter sign-ups, contact forms) to an attacker-controlled MailUp account, resulting in unauthorized collection of user-submitted data such as names, email addresses, and other form fields. Alternatively, the attacker can null the tokens, breaking the MailUp integration entirely and causing a denial-of-service for that functionality. Confidentiality of existing stored data is not directly exposed, but ongoing form-submission data is at risk of exfiltration (GitHub Advisory).

1. Reconnaissance: Identify WordPress sites running the Advanced Form Integration plugin version ≤ 2.6.0 with MailUp integration enabled, using tools like WPScan or by inspecting plugin directories.
2. Obtain low-privilege access: Register or log in as a subscriber-level (or higher) user on the target WordPress site.
3. Navigate to a wp-admin page: Visit any /wp-admin/ page (e.g., /wp-admin/profile.php) while authenticated. This triggers the admin_init hook, which fires the vulnerable token-update handler without authorization checks.
4. Submit crafted request: Send an HTTP POST request to the vulnerable endpoint with attacker-controlled MailUp OAuth token values targeting the adfoin_mailup_keys WordPress option, overwriting the legitimate site tokens.
5. Achieve objective: Future form submissions integrated with MailUp will be routed to the attacker's MailUp account, enabling ongoing data collection; alternatively, submit null/empty token values to disable the integration entirely (GitHub Advisory).

• Logs: WordPress access logs showing authenticated low-privilege users (subscribers) making POST requests to /wp-admin/profile.php or other /wp-admin/ pages with parameters related to MailUp token configuration.
• Database: Unexpected changes to the adfoin_mailup_keys WordPress option in the wp_options table — particularly if the value was modified by a non-administrator user account or at an unusual time.
• Application Behavior: MailUp form submissions suddenly routing to an unknown or unrecognized MailUp account; MailUp integration errors or failures indicating nulled/invalid OAuth tokens.
• User Activity: Subscriber-level accounts accessing /wp-admin/ pages at unusual times or frequencies, especially around the time the adfoin_mailup_keys option was last modified.

Update the Advanced Form Integration plugin to version 2.6.1 or later, which includes the authorization fix released on July 28, 2026. The patch is documented in the plugin's changeset repository (GitHub Advisory). As an interim measure, restrict /wp-admin/ access to trusted users only via server-level controls (e.g., IP allowlisting). After patching, audit the adfoin_mailup_keys WordPress option to confirm the stored OAuth tokens are legitimate and have not been tampered with.

The vulnerability was reported through Wordfence's threat intelligence program and disclosed via the GitHub Advisory Database on July 28, 2026. No significant public researcher commentary, social media discussion, or media coverage beyond standard vulnerability database aggregation has been identified at this time (GitHub Advisory).