Stored XSS in Quill Forms WordPress Plugin 'Other' Field

The Quill Forms | Conversational Multi Step Forms, Surveys & quizzes plugin for WordPress is vulnerable to Stored Cross-Site Scripting via Multiple Choice 'Other' Value in all versions up to, and including, 5.7.1 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. The injected script executes in the context of the WordPress admin results view, making administrators the primary target when reviewing submitted form entries.

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

Quill Forms is a popular WordPress plugin enabling conversational forms, surveys, and quizzes. CVE-2026-15664 is a stored cross-site scripting (XSS) vulnerability in the 'Other' value field of multiple choice questions that affects all versions through 5.7.1. Because the plugin fails to properly sanitize user input and escape output, unauthenticated attackers can inject malicious JavaScript that persists in the database. When administrators or users view the affected form pages, the injected script executes in their browser context, potentially allowing attackers to steal sessions, harvest credentials, or perform unauthorized actions on behalf of logged-in users. This is particularly dangerous because WordPress administrators are high-value targets, and the vulnerability requires no authentication to exploit.

Casky's 754 skills leverage Claude's extended reasoning to map this vulnerability to MITRE ATT&CK techniques TA0001 (Initial Access) and TA0043 (Reconnaissance). When analyzing forms and plugin configurations, Casky detects attack patterns by identifying insufficient input validation controls and missing output encoding in form field handlers—exactly where this XSS exists. Practitioners using Casky would see findings highlighting unescaped user-supplied data in the 'Other' field rendering, flagged as CWE-79 violations. The platform would correlate these code patterns with known exploitation techniques, helping security teams prioritize patching Quill Forms to version 5.7.2 or later and implement Web Application Firewall rules to block malicious script injection attempts targeting form submission endpoints.

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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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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-2026-15664.

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-2026-15664

Casky has 323 skills that investigate the attack patterns behind CVE-2026-15664. Run one and get CVSS-scored findings in 3 minutes.

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