WordPress Post SMTP Plugin Stored XSS in Email Parameters

The Post SMTP – Complete Email Deliverability and SMTP Solution with Email Logs, Alerts, Backup SMTP & Mobile App plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'user_email' parameter in all versions up to, and including, 4.0.1 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. This is exploitable without authentication on WordPress Multisite installations with public registration enabled, as WordPress accepts email addresses containing numeric HTML character references that Post SMTP's stricter validator rejects, persisting the attacker-controlled address verbatim to the email log via the failed-send exception 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

The Post SMTP plugin for WordPress contains a Stored Cross-Site Scripting (XSS) vulnerability in the 'user_email' parameter that allows unauthenticated attackers to inject malicious scripts into the application. Due to insufficient input sanitization and output escaping, these scripts persist in the database and execute whenever any user accesses the affected page, creating a persistent threat vector. This vulnerability affects all versions up to 4.0.1 of a widely-deployed email deliverability plugin, potentially impacting thousands of WordPress installations that rely on this solution for SMTP functionality, email logging, and backup delivery services.

Casky's 754 security skills mapped to MITRE ATT&CK enable detection of the attack patterns underlying this vulnerability through techniques in TA0001 (Initial Access) and TA0043 (Reconnaissance). When analyzing this CVE, practitioners using Casky's Claude AI-powered assessment would identify findings related to parameter injection detection, stored payload analysis, and DOM-based execution patterns. The platform's extended reasoning capabilities map the vulnerability flow to techniques like T1189 (Drive-by Compromise) and T1598 (Phishing: Search Engine), flagging how unauthenticated attackers can inject payloads via email parameters that later execute in user browsers. Practitioners would receive findings highlighting the critical gap between input validation and output encoding, with Casky's skills identifying both the injection point and exploitation conditions, enabling proactive remediation before malicious actors weaponize this vulnerability at scale.

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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-2026-75962.

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

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