CVE-2026-12408: Slim SEO WordPress Information Disclosure

CVE-2026-12408 Overview

CVE-2026-12408 affects the Slim SEO – A Fast & Automated SEO Plugin for WordPress in all versions up to and including 4.9.8. The vulnerability exposes private, draft, pending, future, and password-protected posts through the /wp-json/slim-seo/meta-tags/ai REST API endpoint. Authenticated users with Contributor-level access or higher can retrieve AI-generated summaries of post_content for posts they do not own. The flaw is classified under [CWE-200] Information Exposure.

Critical Impact
Contributor-level attackers can extract substance from private, draft, and password-protected posts authored by other users through the plugin's AI meta-tag REST endpoint.

Affected Products

Slim SEO – A Fast & Automated SEO Plugin For WordPress (versions ≤ 4.9.8)
WordPress sites with the Slim SEO plugin installed and users at Contributor role or above
Any WordPress installation exposing the /wp-json/slim-seo/meta-tags/ai REST route

Discovery Timeline

2026-07-01 - CVE-2026-12408 published to NVD
2026-07-01 - Last updated in NVD database

Technical Details for CVE-2026-12408

Vulnerability Analysis

The vulnerability resides in the AI.php component of the Slim SEO plugin. The REST endpoint /wp-json/slim-seo/meta-tags/ai registers a permission_callback that validates only the top-level edit_posts capability. It does not verify that the authenticated user has read access to the specific post identified by the object.ID parameter in the request body.

When a user calls the endpoint, the generate function forwards the attacker-controlled post ID to Data::get_post_content(). That helper calls the core get_post() function without checking post status, ownership, or password protection. The plugin then feeds the raw post_content into an AI summarization routine and returns the result in the HTTP response body.

This exposes the substance of posts that WordPress would normally restrict, including private posts, drafts, pending items, future-scheduled posts, and password-protected content authored by other users.

Root Cause

The root cause is a broken authorization check [CWE-200]. The permission_callback treats the edit_posts capability as sufficient authorization for any post ID supplied at request time. WordPress requires per-object capability checks such as read_post or edit_post against the specific post ID to enforce ownership and status restrictions. The plugin omits this check and passes the ID directly into content retrieval.

Attack Vector

An authenticated attacker with a Contributor account sends a POST request to /wp-json/slim-seo/meta-tags/ai with a JSON body containing an object.ID value referencing a post owned by another user. The endpoint validates only the coarse edit_posts capability, then invokes Data::get_post_content() for the supplied ID. The response returns an AI-generated summary that discloses the protected content. No user interaction from the victim is required.

Refer to the Wordfence Vulnerability Report and the Slim SEO AI.php source for the vulnerable code paths.

Detection Methods for CVE-2026-12408

Indicators of Compromise

HTTP POST requests to /wp-json/slim-seo/meta-tags/ai originating from Contributor or Author accounts that do not own the referenced posts
Request bodies containing object.ID values referencing posts with post_status of private, draft, pending, future, or password-protected posts
Elevated volumes of REST API calls to the slim-seo/meta-tags/ai route from a single authenticated session

Detection Strategies

Enable WordPress REST API request logging and alert on calls to /wp-json/slim-seo/meta-tags/ai where the requesting user is not the post author
Correlate wp_users role data with post authorship in web access logs to identify cross-author enumeration patterns
Monitor for sequential or scripted iteration through numeric object.ID values in POST bodies to the AI endpoint

Monitoring Recommendations

Ingest WordPress access logs and application logs into a centralized logging platform for correlation across authentication and REST activity
Baseline normal Contributor and Author API usage and alert on deviations targeting the Slim SEO AI route
Track newly created Contributor accounts followed by requests to plugin REST endpoints within short time windows

How to Mitigate CVE-2026-12408

Immediate Actions Required

Update the Slim SEO plugin to a version later than 4.9.8 once the vendor publishes a patched release
Audit user accounts and remove or downgrade unnecessary Contributor-level and higher accounts
Review WordPress access logs for prior requests to /wp-json/slim-seo/meta-tags/ai and identify potentially exposed posts

Patch Information

The vendor changeset is tracked at the Slim SEO plugin changeset 3576523. Administrators should upgrade to the fixed release referenced in the Wordfence Vulnerability Report and confirm the patched version is deployed across all WordPress instances.

Workarounds

Restrict access to the /wp-json/slim-seo/meta-tags/ai REST route at the web application firewall (WAF) or reverse proxy layer until patching
Temporarily deactivate the Slim SEO plugin on multi-author sites where Contributor accounts are untrusted
Enforce least-privilege by limiting REST API access to Editor or Administrator roles through custom permission_callback filters

bash

# Example: block the vulnerable REST route at nginx until patched
location ~ ^/wp-json/slim-seo/meta-tags/ai {
    return 403;
}