Executive Summary

The Ninja Forms plugin for WordPress up to version 3.14.0 has a vulnerability that allows unauthenticated attackers to expose sensitive information. This happens because the plugin unsafely applies the `ninja_forms_merge_tags` filter to user-supplied input within repeater fields, enabling the resolution of `{post_meta:KEY}` merge tags without any authorization checks.

As a result, attackers can extract arbitrary post metadata from any post on the site, including sensitive data such as WooCommerce billing emails, API keys, private tokens, and customer personal information by exploiting the `nf_ajax_submit` AJAX action.

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Impact Analysis

This vulnerability can lead to unauthorized disclosure of sensitive information stored in post metadata on your WordPress site. Attackers can retrieve confidential data such as billing emails, API keys, private tokens, and personal customer information without needing to authenticate.

Such exposure can compromise user privacy, lead to data breaches, and potentially allow further attacks using the leaked credentials or tokens.

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Compliance Impact

I don't know

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Detection Guidance

[{'type': 'paragraph', 'content': 'This vulnerability involves unauthenticated attackers exploiting the `nf_ajax_submit` AJAX action to extract arbitrary post metadata by submitting specially crafted form data containing `{post_meta:KEY}` merge tags. Detection can focus on monitoring HTTP requests to the WordPress site for suspicious AJAX calls to `nf_ajax_submit` that include unusual or unauthorized merge tags in the submitted form data.'}, {'type': 'paragraph', 'content': 'Specifically, you can look for POST requests to the endpoint handling `nf_ajax_submit` with payloads containing the string `{post_meta:` or other merge tags that should not be present in user-submitted data.'}, {'type': 'list_item', 'content': 'Use web server or application firewall logs to filter requests with POST data containing `{post_meta:` or `{user_meta:` targeting the AJAX submission endpoint.'}, {'type': 'list_item', 'content': 'Example command using grep on web server logs (adjust path and log format accordingly):'}, {'type': 'list_item', 'content': "grep -i '{post_meta:' /var/log/apache2/access.log"}, {'type': 'list_item', 'content': "grep -i 'nf_ajax_submit' /var/log/apache2/access.log | grep -i '{post_meta:'"}, {'type': 'paragraph', 'content': 'Additionally, monitoring for unusual spikes in AJAX form submissions or unexpected data patterns in form submissions can help detect exploitation attempts.'}] [4]

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Mitigation Strategies

The primary mitigation is to update the Ninja Forms plugin to version 3.14.1 or later, where the vulnerability has been fixed by disabling merge tag processing on user-submitted values entirely.

If immediate updating is not possible, consider temporarily disabling or restricting access to the AJAX action `nf_ajax_submit` to prevent unauthenticated users from submitting forms that could exploit this vulnerability.

• Update Ninja Forms plugin to version 3.14.1 or newer.
• Restrict or block access to the `nf_ajax_submit` AJAX endpoint for unauthenticated users via web server or firewall rules.
• Monitor logs for suspicious AJAX submissions containing merge tags and respond accordingly.

These steps will prevent unauthenticated attackers from exploiting the unsafe merge tag processing in repeater fields and protect sensitive post metadata from exposure.

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