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CVE-2026-15826 — The User Profile Builder plugin for WordPress is vulnerable to Authentication Bypass via…

Key facts

CVE-2026-15826 is a Critical (9.8) vulnerability: The User Profile Builder plugin for WordPress is vulnerable to Authentication Bypass via…. This entry ships a detection-only PoC and a Docker test lab.
CVE CVE-2026-15826
Severity Critical (9.8)
Detection / prevention —
PoC poc.py
Source 2026/CVE-2026-15826/

Details

English | 한국어

Description

The User Profile Builder plugin for WordPress is vulnerable to Authentication Bypass via Type Confusion in versions up to, and including, 3.16.4. This is due to the wppb_log_in_user() function calling absint() on the return value of wp_insert_user() before performing an is_wp_error() check — when a registration is submitted with a 61–70 character username, WordPress core rejects it with a WP_Error object, but absint() coerces that object to the integer 1 before the error check can short-circuit execution, causing the plugin to bind and return a transient-backed autologin nonce tied to user ID 1. This makes it possible for unauthenticated attackers to log in as the site's Administrator account (user ID 1), resulting in full administrative takeover of the site.

Vulnerability Details

Property Value
CVE ID CVE-2026-15826
Type RCE
CVSS Score 9.8

Proof of Concept

Download

# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2026/CVE-2026-15826/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-2026-15826

# 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/profile-builder/tags/3.16.4/features/functions.php#L1481
  • https://plugins.trac.wordpress.org/browser/profile-builder/tags/3.16.4/front-end/class-formbuilder.php#L262
  • https://plugins.trac.wordpress.org/browser/profile-builder/tags/3.16.4/front-end/class-formbuilder.php#L364
  • https://plugins.trac.wordpress.org/browser/profile-builder/tags/3.16.4/front-end/class-formbuilder.php#L742
  • https://plugins.trac.wordpress.org/browser/profile-builder/tags/3.16.4/front-end/class-formbuilder.php#L945
  • https://plugins.trac.wordpress.org/browser/profile-builder/tags/3.16.4/front-end/default-fields/username/username.php#L28
  • https://plugins.trac.wordpress.org/browser/profile-builder/tags/3.16.4/front-end/default-fields/username/username.php#L49
  • https://plugins.trac.wordpress.org/changeset/3609855/profile-builder
  • https://www.wordfence.com/threat-intel/vulnerabilities/id/9f606fba-f779-42ea-a160-6c3b20dc5e79?source=cve

Generated by PoC Generator on 2026-08-15T18:50:22.717867171

Frequently asked questions

What is CVE-2026-15826?

CVE-2026-15826 is a Critical (9.8) vulnerability: The User Profile Builder plugin for WordPress is vulnerable to Authentication Bypass via…. This entry ships a detection-only PoC and a Docker test lab.

How do I detect CVE-2026-15826?

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-2026-15826?

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.