Executive summary

• Vulnerability: Missing authorization checks allow authenticated users with the Contributor role to request feed deletion actions intended for administrators.
• Likelihood: Low — attacker needs a Contributor account on the site.
• Impact: Low-to-moderate — configured feeds can be deleted, breaking content aggregation and related functionality.
• Immediate mitigations: Deactivate the plugin, restrict Contributor accounts, apply virtual patches at the firewall layer, monitor logs and restore from backups if needed.
• Long-term: Ensure server-side capability and nonce checks in plugin code and enforce least-privilege access for users.

What exactly is wrong?

The plugin exposes a feed-deletion action without proper capability checks (for example, manage_options) and/or nonce verification. Consequently, any authenticated account with Contributor privileges can trigger the deletion routine and remove one or more configured RSS feeds from the plugin settings.

Key points:

• The attack requires authentication; anonymous users cannot exploit it directly.
• A Contributor account is sufficient; many sites grant this role to guest authors or external collaborators.
• No official patch is available at disclosure time; site owners must act defensively.

Why the risk is scored “Low” — and why you should still act

The CVSS score reflects that exploitation requires a pre-existing Contributor account and that the immediate impact is limited to configuration changes. Nevertheless:

• Feed deletion can break public-facing features (aggregated pages, cron jobs, syndicated content).
• If contributor accounts can be created or compromised, the vulnerability becomes more valuable.
• Broken access control is often a first step in chained attacks; remediation reduces overall risk.

Prompt remediation is warranted even for low-severity access-control issues.

Who is affected?

• Sites running WP Filter & Combine RSS Feeds plugin at versions ≤ 0.4.
• Sites that grant Contributor-level permissions to untrusted users.
• Sites without monitoring for plugin configuration changes.

How an attacker could misuse this (high level, non-exploitative)

An attacker with a Contributor account could invoke the plugin’s feed-deletion endpoint (for example via admin-ajax, admin-post, or a REST route) and pass parameters identifying which feed to delete. Effects include missing aggregated content, failed imports, and disrupted editorial workflows. This advisory does not provide proof-of-concept code or step-by-step exploit guidance.

Immediate mitigations (priority order)

1. Deactivate the plugin — If you can tolerate losing its functionality temporarily, remove or deactivate the plugin to eliminate the vulnerable code path.
2. Restrict Contributor accounts — Remove or downgrade guest Contributor accounts and audit user inventory for unknown or inactive users with elevated privileges.
3. Harden registration and authentication — Disable open registration where possible; enforce strong passwords and multi-factor authentication for Contributor+ roles.
4. Adjust role mappings — Ensure only administrators can manage plugin settings by constraining capabilities via a role editor or equivalent control.
5. Virtual patch / WAF rules — Deploy conservative firewall rules that block feed-deletion requests originating from non-admin sessions or lacking valid nonces.
6. Monitor and alert — Enable logging for admin requests and configuration changes; alert on admin-ajax/admin-post and REST deletion attempts from non-admin accounts.
7. Back up plugin settings — Export plugin configuration and take a full site backup now to allow restoration if feeds are removed.

Recommended detection signals (what to look for in logs)

• POST requests to admin-ajax.php or admin-post.php containing parameters like feed_id, action, delete_feed, delete_rss_feed, etc.
• REST API calls to /wp-json/<plugin-namespace>/ with DELETE semantics against feed resources.
• Requests from Contributor accounts resulting in changes to plugin options or database entries storing feed data.
• Unexpected deletion of feed entries in wp_options or plugin-specific tables.
• Audit logs showing non-admin users changing settings.

If you use a web application firewall or logging solution, enable admin-request logging and create alerts for admin-ajax/admin-post actions by accounts without administrator capability.

Safe code-level remediation (for plugin authors or site maintainers)

If you can modify the plugin code, add capability checks and nonce verification to the feed deletion handler. Below is a high-level example — replace function and parameter names with those used by the plugin. Do not deploy untested code to production.

<?php
// Example safe handler for feed deletion
function wpfcr_delete_feed_handler() {
    // Require user to be logged in
    if ( ! is_user_logged_in() ) {
        wp_send_json_error( 'Authentication required', 403 );
        exit;
    }

    // Capability check — only allow administrators / site managers
    if ( ! current_user_can( 'manage_options' ) ) {
        wp_send_json_error( 'Insufficient permission', 403 );
        exit;
    }

    // Verify nonce (replace 'wpfcr_delete_nonce' with plugin's nonce name)
    if ( ! isset( $_POST['wpfcr_nonce'] ) || ! wp_verify_nonce( $_POST['wpfcr_nonce'], 'wpfcr_delete_feed' ) ) {
        wp_send_json_error( 'Invalid request', 400 );
        exit;
    }

    // Sanitize feed ID and perform deletion safely
    $feed_id = isset( $_POST['feed_id'] ) ? intval( $_POST['feed_id'] ) : 0;
    if ( $feed_id <= 0 ) {
        wp_send_json_error( 'Invalid feed id', 400 );
        exit;
    }

    // Delete logic: use prepared calls and WordPress APIs
    // Example: remove from wp_options or custom table depending on plugin
    $deleted = wpfcr_delete_feed_by_id( $feed_id );
    if ( $deleted ) {
        wp_send_json_success( 'Feed deleted' );
    } else {
        wp_send_json_error( 'Could not delete feed', 500 );
    }
    exit;
}
?>

For AJAX/admin_post hooks, ensure both current_user_can() and wp_verify_nonce() checks are present. For REST routes, use a permission_callback enforcing admin-level capability.

Recommended virtual patch / WAF rules

While waiting for a plugin fix, conservative WAF rules can block hazardous requests. Replace parameter names and action values with those actually used by the plugin after inspection. Test rules in staging before production.

1. Block POSTs to admin endpoints that attempt feed deletion without a valid nonce

   Logic (human-readable): If METHOD == POST and URI contains admin-ajax.php or admin-post.php and request body contains feed_id (or similar) and action indicates deletion and no nonce parameter present, then block and log (HTTP 403).

2. Require administrator session or block non-admin attempts

   If request targets known plugin admin pages and is a POST, require the session user role to be administrator; otherwise block or challenge.

3. Rate-limit contributor requests to admin endpoints

   Throttle contributor-role requests to admin-ajax/admin-post endpoints if they exceed a small threshold within a short window.

4. Block REST DELETE calls from non-admin sessions

   Require DELETE on plugin REST endpoints to be issued only by users with admin-level capabilities.

Note: A WAF cannot always validate WordPress nonces reliably. Prefer rules that block requests missing nonce parameters entirely or that originate from non-admin sessions. If your WAF supports session/role awareness, map logged-in sessions to roles and use that to enforce admin-only actions.

How to audit whether you’ve been impacted

1. Inspect plugin settings — verify that configured feeds are present and correct.
2. Check activity logs — look for admin-ajax/admin-post calls and option changes tied to feed settings.
3. Database checks — compare current wp_options (or plugin tables) with backups to detect deletions.
4. Backup comparison — restore or compare backups taken before the disclosure date.
5. Server logs — inspect webserver access logs for relevant POST requests.

Incident response checklist

• Export current configuration and take a full site backup immediately.
• Deactivate the plugin until virtual patches or code fixes are applied.
• Rotate passwords and force logout for non-admin users if account compromise is suspected.
• Restore missing feeds from backups or reconfigure manually.
• Remove any untrusted Contributor accounts and investigate their origin.
• Preserve forensic copies of logs and backups for analysis.
• Notify stakeholders (editors, site owners) of impact and remediation steps.

Secure development recommendations for plugin authors

• Fail closed: deny actions by default and explicitly allow only known-capability holders.
• Use capability checks: current_user_can() with admin-level capabilities or a plugin-specific admin-only capability.
• Verify nonces: use wp_nonce_field() on admin forms and wp_verify_nonce() in handlers.
• Avoid assumptions about roles: always check capabilities at the server side.
• Sanitise and validate inputs: use intval(), sanitize_text_field(), esc_attr(), etc.
• For REST endpoints, implement permission_callback enforcing capability checks.
• Log sensitive actions with user ID, timestamp, IP and parameters.
• Include unit tests for capability checks as part of CI and release process.

Example hardening for REST endpoints

<?php
register_rest_route(
    'wpfcr/v1',
    '/feeds/(?P<id>\d+)',
    array(
        'methods'  => 'DELETE',
        'callback' => 'wpfcr_rest_delete_feed',
        'permission_callback' => function() {
            return current_user_can( 'manage_options' );
        },
    )
);
?>

This ensures DELETE requests are permitted only for users with manage_options capability.

Why virtual patching at the WAF is a good temporary measure

Virtual patching via a firewall is fast, non-destructive when scoped conservatively, provides defence-in-depth, and gives visibility into attempted exploitation. Use it as a temporary control while awaiting a code fix.

Practical checklist for site owners (step-by-step)

1. Identify — confirm plugin is installed and version ≤ 0.4.
2. Backup — take a full site backup (files + database).
3. Deactivate plugin — if feasible, to remove the vulnerable code path.
4. Audit users — remove unknown contributors; enforce password resets for contributors.
5. Deploy WAF rule — block feed deletion actions from non-admins or missing nonce flows.
6. Monitor logs — focus on admin-ajax/admin-post REST calls and option changes.
7. Restore feeds — from backup if necessary.
8. Plan update — apply plugin author patch when available and test before deployment.
9. Post-mortem — document incident and implement process improvements.

Frequently asked questions (FAQ)

Can an anonymous attacker exploit this?

No. Exploitation requires an authenticated account with at least Contributor privileges.

Is site takeover possible using this bug alone?

Not directly. The immediate impact is configuration changes (feed deletion). However, broken access control can be chained with other weaknesses.

How quickly should I act?

Act immediately: deactivate the plugin or apply virtual patches and audit accounts.

What if I depend on this plugin for core site functionality?

Restrict who can manage plugin settings to administrators, deploy conservative firewall rules, and plan to implement a code-level fix or replace the plugin with a maintained alternative.

Long-term remediation & process improvements

• Maintain an inventory of installed plugins and versions.
• Subscribe to vulnerability feeds for critical plugins.
• Have an incident playbook for plugin vulnerabilities (backup, virtual patching, user audit, vendor follow-up).
• Limit Contributor-level access where not strictly required.
• Enforce strong identity controls: 2FA, periodic access reviews and account verification for editorial teams.