CVE-2026-3090 in Post SMTP Plugin
Summary
by MITRE • 03/18/2026
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 ‘event_type’ parameter in all versions up to, and including, 3.8.0 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 vulnerability is only exploitable when the Post SMTP Pro plugin is also installed and its Reporting and Tracking extension is enabled.
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Analysis
by VulDB Data Team • 03/24/2026
The vulnerability identified as CVE-2026-3090 affects the Post SMTP WordPress plugin, specifically targeting versions up to and including 3.8.0. This plugin serves as a comprehensive email deliverability solution that includes SMTP functionality, email logging, alerts, backup SMTP capabilities, and mobile application support. The security flaw manifests as a stored cross-site scripting vulnerability within the plugin's event tracking system, making it particularly concerning for WordPress environments where email delivery and monitoring are critical components of site operations. The vulnerability requires the presence of the Post SMTP Pro plugin along with its Reporting and Tracking extension for exploitation to occur, indicating a specific dependency chain that must be satisfied for the attack vector to be effective.
The technical flaw resides in the insufficient input sanitization and output escaping mechanisms applied to the 'event_type' parameter within the plugin's codebase. This parameter is likely used to categorize and log various email delivery events such as successful sends, failures, or tracking activities. When an attacker can inject malicious JavaScript code through this parameter, the script becomes permanently stored within the plugin's database or configuration files. The vulnerability operates as a stored XSS because the malicious payload is not merely reflected in a response but is instead saved and executed whenever legitimate users access pages containing the injected content. This characteristic transforms what might initially appear as a simple parameter injection flaw into a persistent threat that can affect multiple users over time.
The operational impact of this vulnerability extends beyond simple script execution, as it represents a significant vector for potential compromise within WordPress environments. Attackers can leverage this vulnerability to execute malicious scripts that could steal user sessions, redirect visitors to phishing sites, or even establish persistent backdoors within the affected WordPress installations. The requirement for the Post SMTP Pro plugin and its Reporting and Tracking extension to be enabled creates a specific attack window where organizations must maintain awareness of their plugin configurations and ensure proper security controls are in place. This dependency also suggests that the vulnerability may be more prevalent in environments where advanced email monitoring and reporting features are actively utilized, making it particularly dangerous for businesses that rely heavily on email analytics and delivery tracking.
The exploitation of this vulnerability aligns with common attack patterns documented in the ATT&CK framework under the T1566 technique for "Phishing" and T1059 for "Command and Scripting Interpreter." The stored nature of the XSS makes it particularly effective for delivering malicious payloads that can persist across multiple user sessions and access attempts. Organizations should consider implementing comprehensive input validation and output encoding measures as recommended by CWE-79, which specifically addresses cross-site scripting vulnerabilities. The vulnerability also highlights the importance of proper access controls and privilege separation within WordPress plugin architectures, as the ability to inject code into email tracking systems could potentially allow attackers to manipulate email delivery reports and monitoring data. Security practitioners should implement network-based intrusion detection systems to monitor for suspicious patterns in email tracking parameters and ensure that all WordPress plugins undergo regular security assessments to identify similar input validation weaknesses.
Mitigation strategies for this vulnerability should include immediate plugin updates to versions that address the stored XSS flaw, as well as implementing web application firewalls that can detect and block malicious input patterns targeting the affected parameter. Organizations should also consider disabling the Reporting and Tracking extension if it is not actively required, reducing the attack surface available to potential adversaries. Regular security audits of WordPress installations should include thorough examination of plugin configurations and dependencies to ensure that only necessary extensions are enabled. Additionally, implementing proper content security policies and maintaining updated security monitoring procedures will help detect and prevent exploitation attempts before they can cause significant damage to the affected systems or compromise user data within the WordPress environment.