WordPress Formidable Forms Plugin Arbitrary Code Execution

The Formidable Forms – WordPress Form Builder for Contact Forms, Calculators, Quizzes & More plugin for WordPress is vulnerable to Arbitrary Plugin Installation in all versions up to, and including, 6.35 via the 'file_url' parameter parameter. This is due to insufficient URL prefix validation in validate_url_is_in_s3_bucket() and a permission callback that relies solely on a shared token obtainable by any user with the delegable frm_view_forms capability, without checking install_plugins or activate_plugins capabilities. This makes it possible for authenticated attackers, with subscriber-level access and above, to install arbitrary plugins on the server. Exploitation additionally requires that the site is free-only (Formidable Pro is NOT installed).

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 Formidable Forms WordPress plugin contains a critical vulnerability enabling arbitrary plugin installation through insufficient URL validation and weak permission checks. Attackers can exploit the 'file_url' parameter in the validate_url_is3_bucket() function to bypass S3 bucket restrictions, combined with a permission callback that only verifies a shared token accessible to any user with the frm_view_forms capability—without requiring install_plugins or activate_plugins permissions. This affects all versions up to 6.35 and impacts any WordPress site running the plugin, potentially allowing complete site compromise through malicious plugin installation and execution.

Casky's 754 mapped security skills enable practitioners to detect this attack pattern by correlating MITRE ATT&CK techniques TA0001 (Initial Access) and TA0043 (Reconnaissance). Claude AI's extended reasoning identifies the attack chain: reconnaissance of plugin versions and user capabilities (TA0043), followed by crafted HTTP requests to the vulnerable endpoint with malicious file_url parameters and delegable capability tokens (TA0001). Practitioners using Casky would observe findings flagging anomalous plugin installation attempts originating from low-privilege accounts, suspicious file_url parameter patterns bypassing domain restrictions, and unauthorized capability escalation requests. The skills framework connects these indicators to the specific CWE-74 (Improper Neutralization of Special Elements) root cause, enabling rapid triage and remediation before arbitrary code execution 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-2026-89435.

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-2026-89435

Casky has 323 skills that investigate the attack patterns behind CVE-2026-89435. Run one and get CVSS-scored findings in 3 minutes.

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