Ninja Forms Plugin Stored XSS via Form Data Parameter

The Ninja Forms – Contact Form Builder with Calculators, Quizzes, Signatures & AI Form Builder plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'formData.extra' parameter in all versions up to, and including, 3.15.5 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. The nf_ajax_submit endpoint issues a valid nonce to any requester on failure, effectively neutralizing the nonce check and making exploitation trivially achievable in a single unauthenticated request.

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 the 'formData.extra' parameter affecting all versions through 3.15.5. Attackers can inject malicious JavaScript that persists in the database and executes when legitimate users access affected pages, without requiring authentication. This impacts any WordPress site running vulnerable versions of this widely-deployed form plugin, potentially compromising visitor sessions, stealing credentials, or redirecting users to malicious sites.

Casky's 323 mapped skills leverage Claude's extended reasoning to detect the attack patterns behind this vulnerability across MITRE ATT&CK techniques TA0001 (Reconnaissance) and TA0043 (Reconnaissance). Practitioners using Casky will identify indicators such as suspicious form submissions containing script tags or event handlers in the 'formData.extra' field, anomalous database entries containing encoded JavaScript, and page renders that unexpectedly execute client-side code. The platform's skills enable detection of both initial exploitation attempts (probing form endpoints for sanitization weaknesses) and post-exploitation indicators (monitoring stored payloads in WordPress post/form metadata, analyzing network traffic for JavaScript injection patterns). Security teams gain visibility into the CWE-79 root cause—insufficient input sanitization at the nf_ajax_submit endpoint—allowing them to prioritize patching and implement compensating controls like Web Application Firewalls that filter malicious form submissions before storage.

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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-2026-109997.

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-2026-109997

Casky has 323 skills that investigate the attack patterns behind CVE-2026-109997. Run one and get CVSS-scored findings in 3 minutes.

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