WordPress User Profile Builder Stored XSS in Registration Forms

The User Profile Builder – Beautiful User Registration Forms, User Profiles & User Role Editor plugin for WordPress is vulnerable to Stored Cross-Site Scripting via First Name Field in all versions up to, and including, 4.0.3 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. This vulnerability is only exploitable when the Email Confirmation feature is enabled in Profile Builder.

Casky was already ahead

This CVE exploits attack patterns that Casky's 323matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.

Analysis

CVE-2026-100186 is a Stored Cross-Site Scripting (XSS) vulnerability in the User Profile Builder plugin for WordPress, affecting all versions up to 4.0.3. The vulnerability exists in the First Name field due to insufficient input sanitization and output escaping, allowing unauthenticated attackers to inject malicious scripts that persist in the database. When legitimate users access pages containing the injected payload, the scripts execute in their browsers with their privileges, potentially leading to session hijacking, credential theft, or malware distribution. This is particularly critical because WordPress sites often contain sensitive user data, and the plugin's user registration functionality means attackers can exploit it without prior authentication. Any organization using this plugin version is at risk of compromise, especially if Email Configuration is enabled.

Casky's 323 mapped security skills detect this attack pattern by correlating MITRE techniques TA0001 (Reconnaissance) and TA0043 (Reconnaissance - Search Open Websites/Domains) with CWE-79 exploitation indicators. Claude AI's extended reasoning analyzes attack signatures including: unsanitized form input validation failures, improper output encoding in user profile pages, DOM manipulation patterns indicating script injection attempts, and persistence mechanisms showing stored payloads. Practitioners using Casky would observe findings highlighting suspicious First Name field entries containing script tags, HTML entities, or JavaScript event handlers; detection of payload persistence across page loads; and evidence of script execution contexts during user profile rendering. The platform correlates these indicators with reconnaissance activities that precede exploitation, enabling security teams to identify both active attacks and malicious registrations before they impact users.

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Casky Risk Score

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EPSS Probability

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Shodan Exposure

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GreyNoise Signal

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Composite risk scoring from EPSS, CISA KEV, Shodan, and GreyNoise — 21 security APIs correlated into a single Casky Risk Score. Coming in Casky Pro. Join early access →

323 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-100186.

Abuse of Public-Facing API: Mobile API Abuse

mobile security · low

Run

abusing-dpapi-for-credential-access

red teaming · high

Run

abusing-shadow-credentials-for-privesc

red teaming · high

Run

MITRE ATT&CK Techniques

TA0001 TA0043

Investigate the attack patterns behind CVE-2026-100186

Casky has 323 skills that investigate the attack patterns behind CVE-2026-100186. Run one and get CVSS-scored findings in 3 minutes.

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