Que s'est-il passé (niveau élevé)

A stored XSS vulnerability was found in the Morkva UA Shipping plugin. The plugin accepted input for a “Weight, kg” field and did not properly validate or escape that input before storing it in the database and rendering it later in admin or frontend views. Because the data was stored and later rendered without adequate sanitization, a malicious administrator could inject script content that executes in the context of other administrators viewing the affected pages.

Points clés :

• Attacker prerequisite: an authenticated Administrator account (or another role with capability to edit the affected field).
• Vulnerability type: Stored (persistent) XSS.
• Impact: Execution of attacker-supplied JavaScript in admin pages or frontend pages where the stored field is rendered.
• Fix: Plugin author released version 1.7.10 addressing the input validation and escaping issues.

Why stored XSS matters even for “admin-only” vectors

Administrators are trusted, but that trust is often abused or broken. Consider:

• Admin accounts are commonly compromised via phishing, credential reuse, weak MFA, or stolen sessions.
• Malicious or compromised admins can install backdoors, modify options, install plugins, and exfiltrate secrets.
• Stored XSS persists and executes whenever the infected field is viewed, automatically targeting other privileged users.
• XSS can be used to obtain REST API tokens, change configurations, or install persistent malware.

Even when an issue is “admin-only,” the downstream risk is material and deserves attention.

Analyse technique — ce qui a mal tourné

Root cause summary:

• The plugin accepted a value for a numeric field (weight in kg) but did not validate the input as numeric.
• User-supplied HTML/JS was stored and later echoed into pages without proper escaping or filtering.

Typical faulty pattern (simplified, illustrative):

<?php
// Vulnerable pseudo-code
$weight = $_POST['weight_kg'];
update_option('morkva_weight_kg', $weight); // stores raw input
// later when rendering:
echo get_option('morkva_weight_kg'); // outputs without escaping
?>

Correct approach:

• Validate the field as a number on input (float or int as appropriate).
• Cast or sanitize inputs (e.g., floatval, preg_match for numeric pattern).
• Escape output with appropriate functions (esc_html, esc_attr, number_format) before echoing into HTML context.

Demonstration (safe and educational)

To illustrate without providing an exploitable recipe: if an admin enters a “weight” value containing HTML tags, and the plugin later echoes that value with echo $value; au lieu de echo esc_html( $value );, the browser will parse and execute the tags.

Example of an obviously malicious string (for understanding only):

<script>/* malicious code */</script>

Example of correct handling (sanitization + escaping):

<?php
// On saving input
$weight_input = isset($_POST['weight_kg']) ? $_POST['weight_kg'] : '';
$weight = floatval( str_replace(',', '.', trim( $weight_input )) ); // safer numeric parse
update_option( 'morkva_weight_kg', $weight );

// On output
echo esc_html( number_format( (float) get_option( 'morkva_weight_kg' ), 2 ) );
?>

Restricting the underlying type to numeric values and escaping on output closes the stored XSS avenue.

Scénarios d'exploitation (niveau élevé)

An administrator who controls an account (or who tricks an admin into pasting malicious content) might:

• Inject JavaScript into the weight field that targets other admins to steal cookies or perform actions via admin AJAX endpoints.
• Inject UI elements (fake notices, forms) to capture credentials or social-engineer administrators.
• Create persistence by writing malicious content to other options or by installing a backdoored plugin if the account has install permissions.

Because the injection persists in the database, any admin viewing the affected page may execute the script automatically.

Évaluation des risques

• Attack complexity: Low (requires admin privileges).
• Privilege required: Administrator (or equivalent capability).
• Impact: Potentially high if XSS is used to obtain session cookies, perform admin API calls, or install persistent backdoors.
• Exploitability: Not exploitable by anonymous users; secondary paths (compromised lower-privilege accounts or social engineering) can lead to abuse.

Actions immédiates pour les propriétaires de sites et les administrateurs

If you run Morkva UA Shipping and are on version ≤ 1.7.9:

1. Mettez à jour immédiatement
   • Upgrade the plugin to 1.7.10 or later — this is the single best remediation.
2. If you cannot update right away, temporary options
   • Désactivez le plugin jusqu'à ce que vous puissiez le mettre à jour.
   • Restrict access to admin pages to trusted IPs where feasible.
   • Audit admin accounts: remove unused accounts and enforce unique strong passwords.
   • Enforce multi-factor authentication (MFA) for all admin-level accounts.
3. Scanner et nettoyer
   • Search the database for stored script tags and suspicious inline attributes (e.g., <script, onerror=, onload=, javascript:).
   • If you find suspicious entries, review and remove or neutralize payloads, and reset credentials for affected users.
   • Perform a full site malware scan and integrity check of plugin/theme files.
4. Faire tourner les secrets
   • Force password resets for all admin users, or at minimum reset sessions for accounts that could be exposed.
   • Rotate API keys/tokens used by the site if there’s any suspicion of compromise.
5. Surveillez les journaux
   • Review access logs and admin activity logs for suspicious activity around injection times (new plugin installs, updates, changes to options, large admin POSTs).

Detection and hunting (practical queries and commands)

Safe methods to find potential stored XSS instances introduced via the weight field or elsewhere.

Exemples WP-CLI :

# Search wp_options for <script
wp db query "SELECT option_name, option_value FROM wp_options WHERE option_value LIKE '%<script%';"

# Search postmeta (if plugin stores data in postmeta)
wp db query "SELECT post_id, meta_key, meta_value FROM wp_postmeta WHERE meta_value LIKE '%<script%';"

Grep on an exported DB or backup dump:

grep -R --line-number "<script" db-dump.sql

SQL queries (MySQL):

SELECT option_name, option_value FROM wp_options WHERE option_value RLIKE '<[[:space:]]*script';
SELECT meta_id, post_id, meta_key, meta_value FROM wp_postmeta WHERE meta_value RLIKE '<[[:space:]]*script';

-- Look for event handlers or "javascript:" usage too:
SELECT option_name FROM wp_options WHERE option_value LIKE '%onerror=%' OR option_value LIKE '%javascript:%';

Log analysis tips:

• Inspect webserver access logs for suspicious POSTs to plugin endpoints (e.g., /wp-admin/admin.php?page=morkva-* ou similaire).
• Watch for repeated POST requests with payload-like parameters.

Virtual patching (WAF / firewall rules)

If you cannot update immediately, virtual patching can reduce risk. Test rules in staging to avoid false positives. Examples below target the parameter weight_kg — adjust names to match your environment.

ModSecurity (Core Rule Set style) — block <script in weight_kg

# Block script tags in weight_kg parameter
SecRule REQUEST_METHOD "POST" "chain,phase:2,deny,status:403,id:1000010,msg:'Block stored XSS attempt in weight_kg param',log"
  SecRule ARGS:weight_kg "(?i:(<\s*script|javascript:|onerror|onload|<\s*img|<\s*svg))" "t:none,t:urlDecode"

Generic ModSecurity rule for weight fields (catch variations)

SecRule ARGS_NAMES "(?i)weight(_kg)?|weight_kg" "phase:2,chain,deny,status:403,id:1000011,msg:'Possible XSS in weight field'"
  SecRule ARGS "@rx (?i)(<\s*script|on\w+\s*=|javascript\:)" "t:none,t:urlDecode"

Nginx + Lua WAF pseudo-rule

-- Pseudo-code: inspect POST body for script patterns in "weight_kg"
local body = ngx.req.get_body_data()
if body and string.find(body, "weight_kg=", 1, true) then
  local val = ngx.re.match(body, "weight_kg=([^&]+)")
  if val and ngx.re.find(ngx.unescape_uri(val[1]), "(?i)<\\s*script|javascript:|onerror=", "jo") then
    ngx.exit(ngx.HTTP_FORBIDDEN)
  end
end

Application-layer (WordPress hook) temporary mu-plugin

<?php
// mu-plugin: mu-virtual-patch-morkva.php
add_action( 'admin_init', function() {
    if ( ! empty( $_POST['weight_kg'] ) ) {
        // Force numeric-only: allow digits, optional decimal
        $_POST['weight_kg'] = preg_replace( '/[^0-9\.\,]/', '', $_POST['weight_kg'] );
    }
}, 1 );
?>

Remarques :

• Virtual patching mitigates exploit attempts but is not a replacement for applying the vendor patch.
• Tighten and test regex to avoid blocking valid inputs (decimal separators, localization).
• Monitor denies and tune rules to minimize false positives.

Recommended code-level fixes (for plugin authors / developers)

If your code accepts numeric input, apply these practices:

1. Validate input on save (server-side)

   $weight_raw = isset( $_POST['weight_kg'] ) ? $_POST['weight_kg'] : '';
   $weight_sanitized = str_replace( ',', '.', trim( $weight_raw ) ); // normalize
   if ( preg_match( '/^[0-9]+(?:\.[0-9]+)?$/', $weight_sanitized ) ) {
       $weight = (float) $weight_sanitized;
       update_option( 'morkva_weight_kg', $weight );
   } else {
       // handle invalid input
   }
   

2. Escape output according to context

   $weight = (float) get_option( 'morkva_weight_kg', 0 );
   printf( '<span class="morkva-weight"%3$s kg</span>', esc_html( number_format( $weight, 2 ) ) );
   

3. Use capability checks and nonces for admin forms

   Vérifiez current_user_can() et wp_verify_nonce() on save. Avoid echoing raw $_POST data into admin pages.

4. If HTML is required, use a strict KSES whitelist

   $allowed = array(
     'b' => array(),
     'i' => array(),
     'strong' => array(),
     // be conservative
   );
   
   $clean = wp_kses( $user_input, $allowed );
   update_option( 'some_html_field', $clean );
   

Liste de contrôle de réponse à l'incident (étape par étape)

1. Contention
   • Mettez le site en mode maintenance ou restreignez l'accès.
   • Disable the vulnerable plugin (if patch not applied) or restrict admin access to trusted IPs.
2. Préservez les preuves
   • Take backups of files and database before making changes.
   • Export logs and admin activity records for analysis.
3. Detect payloads
   • Use the DB queries and grep examples above to find stored script tags or event attributes.
   • Inspect option values, postmeta, and plugin-specific tables.
4. Éradication
   • Remove malicious entries carefully, using backups to avoid data loss.
   • Clean or restore affected files from trusted backups.
   • Update plugin to 1.7.10 or remove it if not required.
5. Récupération
   • Reset passwords for all admin-level users.
   • Rotate API keys and tokens that may have been exposed.
   • Re-scan the site for malware and validate integrity.
6. Revue post-incident
   • Identify how any admin account was compromised and close that vector (MFA, password policies, SSO).
   • Hardening: enforce updates, review access controls, and document lessons learned.

Recommandations de durcissement à long terme

• Principle of least privilege: grant admin capabilities only to trusted accounts; use granular roles for day-to-day tasks.
• Enforce strong authentication: mandatory MFA for admin users; consider SSO in enterprise setups.
• Test plugin updates on staging before deploying to production.
• Run scheduled scans and deploy WAF rules that block common injection patterns.
• Implement file integrity monitoring to detect unexpected changes to plugin and theme files.
• Maintain reliable backups and periodically test restores.
• Monitor admin activity and retain logs for forensic analysis.
• Schedule periodic security reviews and penetration tests for high-privilege flows.

Sample ModSecurity signature (log-only tuning)

A conservative ModSecurity rule that logs suspicious input for tuning before switching to deny action:

# Detect suspicious payloads in weight_kg param — log-only (tune before deny)
SecRule ARGS:weight_kg "(?i)(<\s*script|javascript:|on\w+\s*=|<\s*img|<\s*svg)" \
 "phase:2,pass,log,auditlog,id:1000020,severity:2,msg:'Possible stored XSS attempt in weight_kg param',t:none,t:urlDecode"

After a tuning period where false positives are assessed, change the action to refuser if appropriate.

Cleanup scripts and useful utilities

Use WP-CLI or manual inspection to export and clean suspicious options/postmeta. Always backup before mass changes.

# Example: replace <script with &lt;script in wp_options (test with --dry-run)
wp search-replace '