WordPress Mail Catcher Plugin Stored XSS via Error Messages

The Mail logging – WP Mail Catcher plugin for WordPress is vulnerable to Stored Cross-Site Scripting via PHPMailer 'wp_mail_failed' Error Message in all versions up to, and including, 2.1.12 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. Successful exploitation requires a separately installed plugin, such as Contact Form 7, that passes unauthenticated user-controlled input into mail fields whose content PHPMailer will include in its failure error message.

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

WP Mail Catcher, a WordPress plugin for logging email activity, contains a stored cross-site scripting (XSS) vulnerability in how it handles PHPMailer error messages. The vulnerability exists in all versions up to 2.1.12 due to insufficient input sanitization and output escaping. Unauthenticated attackers can inject malicious scripts through error messages generated by related plugins like Contact Form 7—when users later view these logged errors, the scripts execute in their browsers. This affects any WordPress site running the vulnerable plugin alongside email-generating plugins, potentially compromising administrator and user sessions, stealing credentials, or deploying malware.

Casky's 323 matched skills leverage Claude's 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 observe findings correlating improper output encoding in WordPress plugin hooks with script injection points, identify when user-controlled error message data flows unsanitized to database storage and page rendering, and detect the execution context where stored payloads trigger (typically admin pages viewing mail logs). The platform's skill mapping would highlight how attackers bypass authentication requirements by exploiting plugin integration patterns, surface the CWE-79 root cause through code flow analysis, and correlate these signals with reconnaissance activities probing for vulnerable plugin versions—enabling practitioners to prioritize patching and implement output escaping controls before exploitation 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-2026-93889.

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-2026-93889

Casky has 323 skills that investigate the attack patterns behind CVE-2026-93889. Run one and get CVSS-scored findings in 3 minutes.

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