Executive Summary

The vulnerability exists in the NextScripts: Social Networks Auto-Poster plugin for WordPress, specifically in all versions up to and including 4.4.6. It is a Stored Cross-Site Scripting (XSS) vulnerability that occurs via the `[nxs_fbembed]` shortcode.

This vulnerability is caused by insufficient input sanitization and output escaping on the `snapFB` post meta value. Authenticated attackers with Contributor-level access or higher can inject arbitrary web scripts into pages. These scripts execute whenever any user accesses the injected page.

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Detection Guidance

This vulnerability involves Stored Cross-Site Scripting (XSS) via the `[nxs_fbembed]` shortcode in the NextScripts: Social Networks Auto-Poster plugin for WordPress, specifically through the `snapFB` post meta value. Detection involves identifying posts or pages that contain malicious scripts injected via this shortcode.

To detect this vulnerability on your system, you can search your WordPress database for suspicious or unexpected content in the `snapFB` post meta field or look for usage of the `[nxs_fbembed]` shortcode in posts or pages.

• Run a SQL query on your WordPress database to find suspicious `snapFB` meta values, for example: `SELECT * FROM wp_postmeta WHERE meta_key = 'snapFB' AND meta_value LIKE '%<script>%'`
• Search for posts or pages containing the `[nxs_fbembed]` shortcode using WP-CLI: `wp post list --post_type=post,page --format=ids | xargs -I % wp post get % --field=post_content | grep '\[nxs_fbembed\]'`
• Monitor HTTP traffic or logs for suspicious script execution or unexpected Facebook embed content that could indicate exploitation.

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Mitigation Strategies

The primary mitigation step is to update the NextScripts: Social Networks Auto-Poster plugin to version 4.4.7 or later, where the vulnerability has been fixed by enhancing input sanitization and output escaping in the `nxs_fbembed_func` function.

If immediate updating is not possible, consider temporarily disabling or removing the `[nxs_fbembed]` shortcode usage in your posts and pages to prevent exploitation.

Review and sanitize any existing `snapFB` post meta values to remove potentially malicious scripts.

Limit Contributor-level and higher access to trusted users only, as the vulnerability requires authenticated users with at least Contributor privileges.

Implement Web Application Firewall (WAF) rules to detect and block attempts to inject or execute malicious scripts via this plugin.

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Impact Analysis

This vulnerability allows attackers with Contributor-level access or above to inject malicious scripts into WordPress pages via the `[nxs_fbembed]` shortcode. When other users visit these pages, the injected scripts execute in their browsers.

The impact includes potential theft of user credentials, session hijacking, defacement, or redirection to malicious sites. Since the vulnerability is a Stored XSS, the malicious code persists on the site and affects all visitors to the compromised pages.

The CVSS v3.1 base score of 6.4 indicates a medium severity with network attack vector, low attack complexity, requiring privileges, no user interaction, and impacts on confidentiality and integrity.

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Compliance Impact

I don't know

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