Under the Hood: Active Stored XSS in ‘Percent to Infograph’ WordPress Plugin (≤ 1.0) — What Site Owners and Developers Must Do Right Now

Auteur : Expert en sécurité de Hong Kong

Date : 2026-02-13

NOTE: This post is written from the perspective of a Hong Kong security expert. It reviews a recently disclosed stored cross-site scripting (XSS) issue (CVE-2026-1939) affecting the Percent to Infograph plugin (versions ≤ 1.0). The vulnerability requires an authenticated contributor account to inject payloads via shortcode attributes. This article covers risk, detection, immediate mitigations, developer fixes, and longer-term hardening with practical, actionable steps you can apply to protect sites.

Résumé exécutif

• Que s'est-il passé : The Percent to Infograph WordPress plugin (versions ≤ 1.0) contains a stored XSS vulnerability triggered via shortcode attributes. An authenticated user with the Contributor role (or higher) can supply specially crafted data in a shortcode attribute that is stored and later rendered unsafely on the front end.
• Portée : Sites running the affected plugin and allowing Contributor (or higher) accounts to create content are at risk. Because the XSS is stored, any visitor who views the affected page or post can execute the injected script.
• Impact : Persistent XSS can be used for site defacement, redirecting visitors, inserting malicious UI (phishing), or facilitating follow-on attacks (malware injection, unauthorized requests, or session compromise depending on site configuration and token exposure). CVE-2026-1939 has a CVSS score of 6.5 (medium).
• Urgent actions: Remove or disable the plugin if you cannot immediately patch. If you must keep it active, apply short-term mitigations (disable the shortcode output or neutralize it), scan and sanitize content, and restrict contributor privileges. Follow the step-by-step guidance below.

Background: shortcodes, attributes, and why stored XSS is dangerous

WordPress shortcodes let plugin authors insert dynamic output into content by placing bracketed tags like [my_shortcode foo="bar"]. Shortcodes often accept attributes to configure behavior — for example, a percentage value, colors, labels, or links.

The vulnerability arises when a plugin accepts arbitrary attribute values from post content and outputs them directly into HTML without proper validation or escaping. If an attribute value includes scriptable content (for example, embedded HTML with event handlers or javascript : URIs) and the plugin emits it into the page unescaped, that content will be sent to every visitor who loads the page — a classic stored XSS.

Two important factors:

1. An attacker needs an authenticated account with at least Contributor privileges to insert the malicious shortcode attributes into a post or page.
2. The malicious payload is saved in the site database and executed later when the post is viewed — often by administrators, editors, or regular site visitors.

Because the stored payload executes in the site context, an attacker can abuse it to perform harmful actions depending on what the in-page JavaScript can access.

What an attacker can do (attack scenarios)

Stored XSS is powerful because it persists and reaches multiple users. Practical risks include:

• Visitor redirection and fraudulent overlays: Inject JavaScript that redirects visitors to phishing domains or overlays fake login/payment UIs.
• Distribution de logiciels malveillants par téléchargement : Inject scripts that load cryptominers or other malicious payloads.
• Privilege escalation and account takeover: Use XSS to perform actions as logged-in administrators (CSRF + XSS), such as creating admin accounts or changing settings.
• Exfiltration de données : If JavaScript can access non-HttpOnly tokens, analytics cookies, or page-rendered sensitive data, it can exfiltrate that data to attacker servers.
• Mouvement latéral : Use authenticated sessions to plant backdoors, upload files, or alter theme/plugin code.

Note: not every stored XSS leads automatically to full takeover — escalation depends on site configuration, cookie flags, CSRF protections, and what sensitive data is accessible. Nevertheless, stored XSS is a critical entry point and requires immediate attention.

Why Contributor privilege matters — and why it’s not safe

• Many sites accept guest authorship or community contributors; these accounts may be easy to obtain.
• Compromised contributor credentials (reused passwords, phishing) are a common initial foothold.
• Contributors can create posts and insert shortcodes; stored payloads execute when other users view content.
• Insider threats or weak approval workflows increase risk.

Even with a privilege requirement, stored XSS remains a material risk.

Detection: how to find if your site was affected

If you run the affected plugin, assume possible exposure and search for indicators.

1. Search the database for shortcode usage

   Use WP-CLI or direct DB queries to find posts and postmeta that include the plugin’s shortcode tag.

   wp post list --post_type=post,page --format=ids | xargs -n1 -I % wp post get % --field=post_content --format=json | jq -r '.post_content' | grep -n '\[percent'

   Or a DB query (backup first):

   SELECT ID, post_title FROM wp_posts WHERE post_content LIKE '%[percent%';

2. Scan content for script tags or suspicious attributes

   Recherchez <script>, onerror=, onload=, ou javascript : in attributes. Example WP-CLI report:

   wp post list --format=ids | xargs -n1 -I % wp post get % --field=post_content | grep -E -n '<script|onerror=|onload=|javascript:' || echo "no indicators"

3. Check revisions and author activity

   Review post revisions and edits made by contributors during the disclosure window.

   wp post get <id> --field=post_modified
   wp post list --post_type=post --fields=ID,post_author,post_title,post_modified

4. Look for unusual admin behavior and outgoing connections

   Unexpected new admin accounts, file changes, or malicious scheduled events (wp_cron) may indicate further compromise. Scan file integrity and cron entries.

5. Journaux du serveur.

   Check web server logs for suspicious POSTs or repeated content updates. If you operate a WAF, review rule-triggered events for patterns tied to shortcodes.

Always take a full backup before making sweeping changes.

Immediate mitigations (site owner checklist — apply now)

If you run the vulnerable plugin and cannot wait for an official patch, follow these steps in order of impact and ease:

1. Take a full backup (files + DB). Do this before applying any remediation.
2. Deactivate or remove the plugin (fastest, most reliable). If the plugin is not essential, deactivate it until a fixed version is available. This removes the vulnerable shortcode rendering.
3. Neutralize the shortcode (if you must keep the plugin active).

   Replace the plugin’s shortcode handler with a safe no-op so shortcodes remain in content but render nothing. Add to your theme’s functions.php or an mu-plugin:

   <?php
   // Replace 'percent_to_infograph' with the actual shortcode tag used by the plugin
   add_action('init', function() {
       if ( shortcode_exists('percent_to_infograph') ) {
           remove_shortcode('percent_to_infograph');
       }
       // Override with a safe handler returning nothing
       add_shortcode('percent_to_infograph', function($atts, $content = '') {
           return ''; // neutralize all output
       });
   }, 20);

   This prevents any stored payload from executing while leaving content intact for later sanitization.

4. Scan and sanitize stored posts that use the shortcode.

   Identify posts containing the shortcode and either remove dangerous attributes or the shortcode entirely. Export post IDs, review manually, and then update or remove via a safe script.

5. Restrict contributor capabilities and review users.

   Temporarily revoke or tightly control Contributor or higher privileges. Require strong passwords and, where possible, multi-factor authentication for content creators and admins.

6. Harden content moderation workflows.

   If you accept remote contributors, enforce editorial review before content goes live.

7. Add a Content Security Policy (CSP) to limit impact.

   CSP is not a replacement for proper escaping, but a restrictive CSP (disallowing inline scripts) raises the bar:

   Content-Security-Policy: default-src 'self'; script-src 'self' https://trusted-cdn.example.com; object-src 'none'; base-uri 'self'; frame-ancestors 'none';

   Deploy CSP in report-only mode first to discover site breakage.

8. Monitor for signs of exploitation. Review web logs, outgoing XHRs to suspicious domains, and recent administrative changes.

Cleaning up stored content safely

Sanitizing existing posts requires care — always backup and test on staging.

1. Export affected posts to a staging site and perform sanitization there.
2. Use a script to parse content, find shortcode matches, validate attributes, and remove dangerous parts. Example (run in a WP environment and test first):

<?php
// This script should be run in a WP environment (wp eval-file) and tested on staging
$shortcode_tag = 'percent_to_infograph';
$posts = get_posts(array(
    'post_type' => array('post', 'page'),
    'posts_per_page' => -1,
    's' => '[' . $shortcode_tag
));
foreach ($posts as $post) {
    $content = $post->post_content;
    // Very conservative: remove all occurrences of the shortcode entirely
    $content = preg_replace('/\[' . $shortcode_tag . '[^\]]*\]/i', '', $content);
    // Alternatively: parse shortcode_atts() and sanitize each attribute individually
    wp_update_post(array(
        'ID' => $post->ID,
        'post_content' => $content
    ));
}

After sanitization on staging and verification, migrate cleaned content to production. For many posts use scripted cleanups but always manually validate samples.

Developer guidance: how to fix shortcodes to prevent XSS

For plugin authors and developers, proper input validation and context-aware escaping are essential. Key rules:

1. Validate and normalize attributes early. Utilisez shortcode_atts() to set defaults and whitelist expected attributes. Cast numeric attributes and validate color formats.
2. Escape all output according to context.
   • Contexte des attributs HTML : esc_attr()
   • HTML element content context: esc_html()
   • If allowing limited HTML, use wp_kses() avec une liste d'autorisation stricte.

   Example safe rendering:

   $atts = shortcode_atts(array(
       'label' => '',
       'value' => '0',
       'color' => '#000000'
   ), $atts, 'percent_to_infograph');
   
   $label = sanitize_text_field($atts['label']);
   $value = intval($atts['value']);
   // Basic hex color validation
   $color = preg_match('/^#[0-9a-fA-F]{3,6}$/', $atts['color']) ? $atts['color'] : '#000000';
   
   // Output safely
   echo '<div class="pt-infograph">';'<span class="pt-label">' . esc_html($label) . '</span>';'<span class="pt-value" style="color:' . esc_attr($color) . '">' . esc_html($value) . '%</span>';'</div>';

3. Avoid outputting raw HTML or attribute strings that came directly from user content.
4. Utilisez wp_kses_post() or a strict wp_kses allowlist for limited HTML.
5. Add automated tests and static analysis to detect unsafe output patterns.
6. Sanitize at the earliest point possible. Apply sanitization on input/save where appropriate, not only on output.

If a plugin must accept rich HTML for an advanced attribute, implement server-side whitelisting or an admin approval workflow before publishing.

WAF and virtual patching — what a firewall can do (neutral, tactical guidance)

While the upstream patch is the correct long-term fix, a Web Application Firewall (WAF) or similar filtering layer can provide short-term virtual patching:

• Block POST requests that attempt to save shortcode attributes containing script markers (e.g., <script>, onerror=, onload=, javascript :) when created by lower-privilege accounts.
• Inspect and sanitize content parameters in REST API or admin POSTs that update post content.
• Deploy rules targeting patterns specific to the effected shortcode tag to reduce false positives.
• Flag and throttle contributors submitting content with suspicious payload patterns.

Example conceptual detection rule (description only): if a request updating post content contains the shortcode tag and attribute values with script-like markers, block or require additional verification.

Monitoring and long-term hardening

1. Minimize users with publish/edit capabilities; apply least privilege.
2. Require strong authentication and two-factor authentication for anyone who can publish content.
3. Run periodic automated scanning (SAST/DAST) on production and staging to detect XSS and other injection vectors.
4. Use a content security policy (CSP) tuned for your site to mitigate impact of potential XSS.
5. Implement file integrity monitoring, change detection, and centralized logging for faster detection.
6. Maintain a vulnerability disclosure process for third-party plugin developers and subscribe to security intelligence feeds.
7. Use staging environments for plugin/theme updates and run security tests before deploying to production.

Divulgation responsable et calendrier

The issue was researched and reported by an independent researcher and assigned CVE-2026-1939. At time of disclosure there was no public upstream patch for versions ≤ 1.0; assume unpatched risk and apply mitigations.

If you are a plugin developer: coordinate with the researcher to reproduce, provide a timely patch, and publish clear remediation instructions. If you are a site owner: prefer patching on release but apply virtual patches and hardening in the meantime.

Practical examples: quick commands and scripts (safe, non-exploit)

Safe operational examples (test on staging):

wp db query "SELECT ID, post_title FROM wp_posts WHERE post_content LIKE '%[percent_to_infograph%'" --skip-column-names

add_action('init', function() {
    if (shortcode_exists('percent_to_infograph')) {
        remove_shortcode('percent_to_infograph');
    }
    add_shortcode('percent_to_infograph', function($atts) {
        return ''; // neutralized
    });
}, 20);

wp post list --format=ids | xargs -n1 -I % sh -c 'wp post get % --field=post_content | grep -E -n "<script|onerror=|onload=|javascript:" && echo "post id: %"' || true

Use these tools only if you understand WP-CLI and backup workflows.

Wrap up and checklist (operate from a secure posture)

If you run the affected Percent to Infograph plugin (≤ 1.0), follow this prioritized checklist now:

1. Backup your site (files + DB).
2. Deactivate/remove the plugin if you can.
3. If you must keep it active, neutralize its shortcode handler while you sanitize content.
4. Identify and sanitize any posts/pages that contain the plugin shortcode.
5. Review and restrict Contributor (and higher) accounts; enforce strong auth and 2FA.
6. Implement a CSP and make cookies HttpOnly/Secure/SameSite where practical.
7. Run a malware scan and monitor logs for suspicious activity.
8. Consider short-term virtual patching or WAF policies while you remediate.

Stored XSS lets attackers persist payloads in your database and reach users without repeated attempts. Even if a patch is pending, the layered actions above will reduce exposure and buy time to apply a complete fix.

Restez vigilant — Expert en sécurité de Hong Kong