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Atomicorp WAF Research Note: CVE-2026-4406

Gravity Forms <= 2.9.30 - Reflected Cross-Site Scripting via ‘form_ids’ Parameter

CVE Details

Status: Attack Blocked by Atomicorp
  • Already protected by existing Atomicorp WAF rules
  • Protection status: Understanding Atomicorp WAF Protection Status
  • CVE: CVE-2026-4406
  • Name: Gravity Forms <= 2.9.30 - Reflected Cross-Site Scripting via ‘form_ids’ Parameter
  • Severity: Medium
  • CVSS: 4.7 (v3.1) (Medium)
  • CVSS version: 3.1
  • CVSS source: Wordfence CNA
  • CVSS vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N
    • Attack vector: Network
    • Attack complexity: High
    • Privileges required: None
    • User interaction: Required
    • Scope: Changed
    • Confidentiality impact: Low
    • Integrity impact: Low
    • Availability impact: None
  • CWE: CWE-79
  • Vendor: Gravity Forms
  • Vulnerable product: Gravity Forms
  • CVE published: 2026-04-08
  • CVE last modified: 2026-07-24
  • Latest Update: 2026-09-14
  • Selected Rule IDs observed: 340087 , 340099 , 341099 , 341266 , 346755
  • Matching rules: 5; rules with blocking actions: 5
  • Would-block Rule IDs: 340087 , 340099 , 341099 , 341266 , 346755
  • Request surfaces inspected: JSON request data, Request URI, Request argument names, Request arguments, Request cookies, Request filename, Request headers, SOAP request data

Vulnerability Description

The Gravity Forms plugin for WordPress is vulnerable to Reflected Cross-Site Scripting via the form_ids parameter in the gform_get_config AJAX action in all versions up to, and including, 2.9.30. This is due to the GFCommon::send_json() method outputting JSON-encoded data wrapped in HTML comment delimiters using echo and wp_die(), which serves the response with a Content-Type: text/html header instead of application/json. The wp_json_encode() function does not HTML-encode angle brackets within JSON string values, allowing injected HTML/script tags in form_ids array values to be parsed and executed by the browser. The required config_nonce is generated with wp_create_nonce('gform_config_ajax') and is publicly embedded on every page that renders a Gravity Forms form, making it identical for all unauthenticated visitors within the same 12-hour nonce tick. 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 vulnerability cannot be exploited against users who are authenticated on the target system, but could be used to alter the target page.

  1. Maintain the observed Atomicorp protections. Keep your Atomicorp commercial rules current and confirm that the selected observed rules (340087 , 340099 , 341099 , 341266 , 346755 ) have not been locally disabled. Atomicorp commercial rules are enabled by default. If you use Atomic WAF, review the applicable policy and rule settings.

  2. Apply the vendor’s remediation. WAF protection is defense in depth and does not replace upgrading or following the affected vendor’s guidance.

    • Affected versions: Gravity Forms versions through 2.9.30.
    • No specific CNA/vendor solution or workaround is included in the current CVE Record . Review the vendor’s security advisories and supported-release guidance before making changes.

  3. Validate after changes. Confirm rule updates are current, review WAF events for the affected application, and test application behavior after vendor upgrades, mitigations, or local policy changes.

Research Notes

Atomicorp WAF protections are designed around attack techniques and exploit behaviors, allowing existing protections to apply across multiple vulnerabilities without requiring a unique rule for every CVE.

Public Vulnerability References

Test or Research Source

  • Source: Atomicorp AI Research Framework
  • Tags: cve, derived, waf-probe, xss

Research Note Context

This research note documents exploit-technique analysis associated with this vulnerability and references Atomicorp WAF protections observed during engineering review, testing, or validation activities.

Atomicorp security controls are generally designed to identify and mitigate attack techniques and exploit behaviors rather than individual CVE identifiers. As a result, protections developed for one vulnerability may also apply to related attack variants and future vulnerabilities using similar techniques.

Learn More

Atomicorp develops commercially supported security technologies for web applications, servers, endpoints, workloads, and legacy enterprise platforms.

Organizations interested in protecting systems against exploit techniques associated with vulnerabilities such as this one can learn more about:

  • Atomic ModSecurity Rules: commercially maintained WAF rules for ModSecurity deployments, including protections for web attacks, bots, scanners, malware, exploitation attempts, and emerging vulnerability classes.
  • Atomic WAF: an enterprise web application firewall with Atomicorp rules, centralized management, reporting, authentication controls, and operational tooling.
  • Atomic ModSecurity Integrator: a special licensing option for MSPs, MSSPs, OEMs, VARs, reverse proxy providers, and other integrators who want to incorporate Atomicorp ModSecurity rule technology into their own products or services.
  • Atomic OSSEC: an enterprise OSSEC-based intrusion detection, compliance, and security monitoring platform.
  • Atomic Protector: workload protection for Linux, web, cloud, data center, and hybrid environments.

For additional information, product evaluations, or technical discussions, visit https://www.atomicorp.com/ or https://modsecurity.io/ .