WordPress Mailchimp Plugin Stored XSS via Merge Fields

The Connect Contact Form 7 and Mailchimp plugin for WordPress is vulnerable to Stored Cross-Site Scripting via Mailchimp Merge Field Values in all versions up to, and including, 0.9.78.06 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 payload is only triggered when a privileged user (Administrator) performs a Contact Lookup for the email address submitted via the CF7 form, meaning execution is deferred until an administrator interacts with the affected entry.

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-2026-15000 is a Stored Cross-Site Scripting (XSS) vulnerability in the Connect Contact Form 7 and Mailchimp plugin for WordPress affecting all versions up to 0.9.78.06. The vulnerability stems from insufficient input sanitization and output escaping of Mailchimp Merge Field values, allowing unauthenticated attackers to inject arbitrary JavaScript code into pages. When a privileged administrator interacts with the form, the malicious payload executes in their browser session, potentially enabling account takeover, privilege escalation, or lateral movement within the WordPress environment. This affects any WordPress site using this plugin, making it a critical risk for organizations managing customer forms and email marketing integrations.

Casky's 322 matching security skills leverage Claude AI with extended reasoning to detect the attack patterns underlying this vulnerability across MITRE ATT&CK techniques TA0001 (Initial Access) and TA0043 (Reconnaissance). Practitioners using Casky would identify detection patterns such as: anomalous input values in Mailchimp merge field submissions containing script tags or encoded JavaScript, unusual DOM manipulation events triggered by form processing, and privilege escalation indicators when administrator sessions execute unexpected client-side code. The platform's skill mapping correlates CWE-79 (Improper Neutralization of Input During Web Page Generation) with specific reconnaissance and exploitation behaviors, enabling teams to spot attempted injections before they persist and to trace attack chains back to initial compromise vectors in their WordPress infrastructure.

Live Threat IntelligenceComing soon

Casky Risk Score

—

EPSS Probability

—

Shodan Exposure

—

GreyNoise Signal

—

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-2026-15000.

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-2026-15000

Casky has 322 skills that investigate the attack patterns behind CVE-2026-15000. Run one and get CVSS-scored findings in 3 minutes.

Run the skill that detects this →

X Instagram LinkedIn