Ninja Forms Plugin Stored XSS via Type Confusion

The Ninja Forms – The Contact Form Builder That Grows With You plugin for WordPress is vulnerable to Stored Cross-Site Scripting via Repeater Child 'type' Confusion via Unmatched Array Key in all versions up to, and including, 3.15.1 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. Exploitation requires the Ninja Forms File Uploads add-on to be active, as the attack routes the unwhitelisted child entry through the File Uploads handler to write an attacker-supplied HTML file containing arbitrary JavaScript into any web-server-writable directory, including the site root, where it is served from the site's own origin.

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

The Ninja Forms Contact Form Builder plugin for WordPress contains a stored cross-site scripting (XSS) vulnerability in its Repeater Child functionality, where insufficient input sanitization and output escaping allow unauthenticated attackers to inject malicious scripts. This vulnerability is particularly dangerous because it's stored—meaning the malicious payload persists in the database and executes for every user who accesses the affected page, creating a widespread attack surface. Any WordPress site using Ninja Forms versions up to 3.15.1 with the File Uploads extension enabled is vulnerable, potentially affecting thousands of websites and their visitors who may unknowingly execute attacker-controlled JavaScript in their browsers.

Casky's 323 mapped security skills leverage Claude's extended reasoning to detect the attack patterns underlying this CVE across MITRE ATT&CK techniques TA0001 (Initial Access) and TA0043 (Reconnaissance). Practitioners using Casky would identify detection opportunities across multiple layers: input validation bypass detection (CWE-79 patterns), where type confusion in array keys allows malicious 'type' parameters to bypass sanitization filters; data flow analysis revealing unsanitized user input flowing directly to output without escaping; and behavioral analysis of stored payload execution patterns. When this vulnerability is exploited, Casky's skill framework would highlight suspicious form submission patterns, unusual JavaScript injection attempts in form field metadata, and the characteristic DOM-based execution signatures that distinguish this stored XSS from reflected variants—enabling security teams to pinpoint compromised forms and prioritize remediation before widespread user impact occurs.

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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-2026-19769.

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-2026-19769

Casky has 323 skills that investigate the attack patterns behind CVE-2026-19769. Run one and get CVSS-scored findings in 3 minutes.

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