Contact Form 7 Plugin File Upload Validation Bypass

The Drag and Drop Multiple File Upload for Contact Form 7 WordPress plugin before 1.3.9.9 does not validate the final name of an uploaded file after stripping characters from it, allowing unauthenticated users to defeat its file type restrictions and execute arbitrary code on the server.

Casky was already ahead

This CVE exploits attack patterns that Casky's 322matched 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

CVE-2026-18781 exploits insufficient file validation in the Drag and Drop Multiple File Upload plugin for WordPress Contact Form 7. The vulnerability stems from CWE-94 (Improper Control of Generation of Code), where the plugin strips certain characters from uploaded filenames but fails to re-validate the final filename before processing. This allows unauthenticated attackers to bypass file type restrictions—for example, uploading a malicious PHP file by initially naming it with characters that, once stripped, result in an executable extension. With a CVSS score of 8.1, this is a critical risk for any WordPress installation using this plugin, potentially enabling remote code execution on thousands of websites that rely on Contact Form 7 for customer communications.

Casky's 322 mapped skills detect the attack patterns associated with TA0001 (Reconnaissance) and TA0043 (Resource Development) by analyzing file upload anomalies and code generation behaviors through Claude AI with extended reasoning. Practitioners using Casky would see detection signals including: suspicious filename transformations where character stripping reveals executable extensions, POST requests to the plugin's upload handlers with polyglot or encoding-obfuscated filenames, and unusual file creation patterns in web-accessible directories. The platform's skills correlate these signals with known exploitation patterns—identifying when attackers probe file validation logic before launching payload uploads—allowing security teams to block attacks before code execution occurs and to identify compromised installations for incident response.

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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 →

322 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-18781.

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-2026-18781

Casky has 322 skills that investigate the attack patterns behind CVE-2026-18781. Run one and get CVSS-scored findings in 3 minutes.

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