CVE-2026-13439: WordPress Easy Form Builder Unauthenticated Privilege Escalation (CVSS 9.8)

Vulnerability Overview

A critical unauthenticated privilege escalation vulnerability has been identified in the Easy Form Builder by WhiteStudio plugin for WordPress. Tracked as CVE-2026-13439 with a CVSS score of 9.8, the flaw allows any unauthenticated attacker to escalate their privileges to administrator level on affected WordPress sites — effectively achieving full site takeover without any credentials.

Vulnerability Summary

Technical Details

The vulnerability exists in the plugin's password recovery flow. Specifically, the plugin uses the publicly-visible session identifier (sid) as the password reset token, which is stored and accessible without authentication.

Root Cause

The password reset mechanism stores a session identifier (sid) that is visible to unauthenticated users. This token is then used as the password reset credential, meaning any attacker who can observe or enumerate the sid value can initiate a password reset for any account — including administrator accounts.

Vulnerable Flow:
1. Attacker accesses publicly visible session identifier (sid)
2. Attacker supplies sid as the password reset token
3. Plugin validates reset token against sid (no auth check)
4. Attacker resets administrator password
5. Attacker logs in as administrator

Attack Complexity

The attack requires no authentication and is network-accessible, giving it the maximum attack vector rating. The session identifier being publicly visible makes exploitation straightforward for technically capable attackers.

Impact

A successful exploit grants the attacker full WordPress administrator access, enabling:

• Complete site takeover — modify pages, install plugins, change theme
• Backdoor installation — drop PHP shells or malicious plugins
• Data exfiltration — access all site data, user records, form submissions
• SEO spam injection — redirect visitors, inject spam links
• Ransomware deployment — encrypt or delete site files
• Lateral movement — use the compromised server to pivot further into the hosting environment

Affected Software

Sites running version 4.0.11 or earlier of this plugin with it active are potentially vulnerable.

Detection

Check Plugin Version

# Via WP-CLI
wp plugin get ws-form --fields=name,version,status
 
# Or check the plugin readme
cat wp-content/plugins/easy-form-builder/readme.txt | grep "Stable tag"

Check for Suspicious Admin Accounts

-- Identify recently created administrator accounts
SELECT u.user_login, u.user_email, u.user_registered
FROM wp_users u
JOIN wp_usermeta m ON u.ID = m.user_id
WHERE m.meta_key = 'wp_capabilities'
  AND m.meta_value LIKE '%administrator%'
ORDER BY u.user_registered DESC;

Log Review

# Look for password reset activity in plugin logs or access logs
grep -i "easy-form-builder\|ws-form" /var/log/nginx/access.log | grep -i "reset\|sid"

Remediation

Immediate Action

1. Update the plugin to the latest version available from the WordPress plugin repository. If a patched version is not yet available, deactivate and remove the plugin immediately.

# Update via WP-CLI
wp plugin update easy-form-builder
 
# Or deactivate if no patch exists
wp plugin deactivate easy-form-builder

2. Audit administrator accounts — remove any suspicious or unrecognized admin accounts.

# List all admins
wp user list --role=administrator --fields=ID,user_login,user_email,user_registered
 
# Delete suspicious account
wp user delete <ID> --reassign=<valid_admin_id>

3. Reset all administrator passwords as a precaution.

wp user reset-password $(wp user list --role=administrator --field=user_login)

Longer-Term Hardening

1. WordPress Hardening
   - Keep all plugins, themes, and WordPress core updated
   - Remove unused plugins — reduce attack surface
   - Use a WAF (Wordfence, Sucuri) to block exploit attempts
   - Enable two-factor authentication for admin accounts

2. Monitoring
   - Enable admin activity logging (WP Activity Log plugin)
   - Alert on new administrator account creation
   - Monitor for unusual file modifications in wp-content/

3. Network Controls
   - Restrict wp-admin access by IP where possible
   - Block XML-RPC if not required

References

• NVD — CVE-2026-13439
• WordPress Plugin Repository — Easy Form Builder
• Wordfence Threat Intelligence

Published: July 21, 2026. Update this advisory as patch availability changes.

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• WordPress WP2Shell Plugin Under Mass Exploitation
• Critical WPvivid Backup Plugin RCE (CVE-2026-1357)