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CVE-2026-75957 — The Ultimate Multisite – WordPress Multisite SaaS & WaaS Platform plugin for WordPress is…

Key facts

CVE-2026-75957 is a Critical (9.8) vulnerability: The Ultimate Multisite – WordPress Multisite SaaS & WaaS Platform plugin for WordPress is…. This entry ships a detection-only PoC and a Docker test lab.
CVE CVE-2026-75957
Severity Critical (9.8)
Detection / prevention —
PoC poc.py
Source 2026/CVE-2026-75957/

Details

English | 한국어

Description

The Ultimate Multisite – WordPress Multisite SaaS & WaaS Platform plugin for WordPress is vulnerable to Authentication Bypass in all versions up to, and including, 2.15.0 via the checkout_form parameter of the login_customer_after_checkout function. This is due to the publicly accessible wu_ajax_nopriv_wu_validate_form AJAX handler accepting a freely obtainable checkout nonce, and the checkout_form=wu-finish-checkout parameter causing get_validation_rules() to discard all validation rules while finish_checkout_form_fields() returns an empty step list — forcing is_last_step() to return true and routing the request directly into full order processing — after which maybe_create_customer() resolves the attacker-supplied email_address to an existing WordPress user ID without any authentication or ownership verification, and login_customer_after_checkout() calls wp_set_auth_cookie() for that user ID via a passwordless code path. This makes it possible for unauthenticated attackers to log in as any existing WordPress user — including a Network Super Admin — simply by knowing their email address. Exploitation requires that the targeted user account has no pre-existing Ultimate Multisite customer record; accounts such as a Network Super Admin on a fresh Multisite install, or any administrator or editor added before Ultimate Multisite was configured, satisfy this condition and are therefore exploitable.

Vulnerability Details

Property Value
CVE ID CVE-2026-75957
CVSS Score 9.8

Proof of Concept

Download

# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2026/CVE-2026-75957/poc.py

Usage

# Run PoC against target
python3 poc.py --target <TARGET_URL>

# With authentication
python3 poc.py --target <TARGET_URL> --username <USER> --password <PASS>

⚠️ Warning: This PoC is for authorized security testing only. It uses detection-only techniques and does not exploit or damage target systems.

Test Lab

This repository includes a Docker-based test environment with both vulnerable and patched applications.

Quick Start

# Clone and navigate to CVE directory
cd CVE-2026-75957

# Start both applications
docker-compose up -d

# Run tests
./run-tests.sh    # Linux/Mac
./run-tests.ps1   # Windows PowerShell

Application Endpoints

Application URL Status
Vulnerable App http://localhost:8080 Shows vulnerability
Patched App http://localhost:8081 Demonstrates fix

Directory Structure

├── README.md           # English documentation
├── README_KO.md        # Korean documentation
├── poc.py              # PoC detection script
├── docker-compose.yml  # Container orchestration
├── run-tests.sh        # Linux/Mac test runner
├── run-tests.ps1       # Windows test runner
├── vulnerable-app/     # Vulnerable version
│   ├── app.py
│   ├── Dockerfile
│   └── requirements.txt
└── patched-app/        # Fixed version
    ├── app.py
    ├── Dockerfile
    └── requirements.txt

References

  • https://plugins.trac.wordpress.org/browser/ultimate-multisite/tags/2.14.2/inc/checkout/class-checkout.php#L1223
  • https://plugins.trac.wordpress.org/browser/ultimate-multisite/tags/2.14.2/inc/checkout/class-checkout.php#L208
  • https://plugins.trac.wordpress.org/browser/ultimate-multisite/tags/2.14.2/inc/checkout/class-checkout.php#L2489
  • https://plugins.trac.wordpress.org/browser/ultimate-multisite/tags/2.14.2/inc/checkout/class-checkout.php#L2700
  • https://plugins.trac.wordpress.org/browser/ultimate-multisite/tags/2.14.2/inc/models/class-checkout-form.php#L1352
  • https://plugins.trac.wordpress.org/browser/ultimate-multisite/tags/2.15.0/inc/checkout/class-checkout.php#L1223
  • https://plugins.trac.wordpress.org/browser/ultimate-multisite/tags/2.15.0/inc/checkout/class-checkout.php#L208
  • https://plugins.trac.wordpress.org/browser/ultimate-multisite/tags/2.15.0/inc/checkout/class-checkout.php#L2489
  • https://plugins.trac.wordpress.org/browser/ultimate-multisite/tags/2.15.0/inc/checkout/class-checkout.php#L2700
  • https://plugins.trac.wordpress.org/browser/ultimate-multisite/tags/2.15.0/inc/models/class-checkout-form.php#L1352
  • https://plugins.trac.wordpress.org/changeset/3653622/ultimate-multisite/trunk/inc/checkout/class-checkout.php
  • https://plugins.trac.wordpress.org/changeset?reponame=&new=3653623%40ultimate-multisite%2Ftags%2F2.15.1&old=3634394%40ultimate-multisite%2Ftags%2F2.15.0
  • https://www.wordfence.com/threat-intel/vulnerabilities/id/66cb8c6f-d405-4115-a626-040e9b5b1e62?source=cve

Generated by PoC Generator on 2026-10-04T05:58:41.989541374

Frequently asked questions

What is CVE-2026-75957?

CVE-2026-75957 is a Critical (9.8) vulnerability: The Ultimate Multisite – WordPress Multisite SaaS & WaaS Platform plugin for WordPress is…. This entry ships a detection-only PoC and a Docker test lab.

How do I detect CVE-2026-75957?

Run the detection-only PoC included with this entry against your Docker test lab to confirm whether a target is affected; pair it with your own IDS logging.

How do I block or mitigate CVE-2026-75957?

Upgrade to a fixed version per the vendor advisory; the NVD record lists the affected versions. Use the included PoC to verify your remediation.

For authorized security testing and research only. See the full source and NVD record.