CVE-2023-3087 in FluentSMTP Plugin
Summary
by MITRE • 07/12/2023
The FluentSMTP plugin for WordPress is vulnerable to Stored Cross-Site Scripting via an email subject in versions up to, and including, 2.2.4 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.
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Analysis
by VulDB Data Team • 07/25/2023
The FluentSMTP plugin for WordPress represents a widely used email delivery solution that integrates seamlessly with WordPress environments to handle email sending functionality. This particular vulnerability affects versions up to and including 2.2.4, where the plugin fails to properly sanitize user input when processing email subjects. The flaw exists within the plugin's handling of email metadata, specifically in how it processes and stores subject lines that are submitted through the WordPress admin interface or other integration points. The vulnerability stems from inadequate input validation mechanisms that allow malicious actors to inject potentially harmful script code into email subject fields without proper sanitization.
The technical implementation of this stored cross-site scripting vulnerability occurs when an attacker crafts a malicious email subject containing embedded script code and submits it through the plugin's interface. The plugin stores this malformed input without adequate sanitization or escaping, creating a persistent vector for attack. When administrators or other users view the email records in the WordPress admin panel or other interfaces that display these stored email subjects, the malicious scripts execute within the context of the user's browser session. This execution occurs because the plugin fails to properly escape output when rendering these stored subject lines, violating fundamental security principles of input validation and output encoding. The vulnerability is classified as a stored XSS issue because the malicious payload persists in the plugin's database and executes each time the affected page is loaded.
The operational impact of this vulnerability extends beyond simple script execution, as it creates a persistent threat vector that can be exploited by unauthenticated attackers to compromise user sessions and potentially escalate privileges. Attackers can craft malicious email subjects that, when viewed by administrators, could steal session cookies, redirect users to phishing sites, or execute other malicious actions within the context of the WordPress admin environment. The vulnerability is particularly concerning because it requires no authentication to exploit, making it accessible to anyone who can submit data through the plugin's interface. This creates a significant risk for WordPress installations where the plugin is used for managing email communications, as administrators frequently access email records and may inadvertently trigger the malicious script execution. The vulnerability can be leveraged to perform actions such as modifying email configurations, accessing sensitive data, or even taking full control of administrator sessions through session hijacking techniques.
Security professionals should immediately update to version 2.2.5 or later of the FluentSMTP plugin to address this vulnerability, as this release includes proper input sanitization and output escaping mechanisms. Organizations should also implement additional monitoring for suspicious email subject entries and consider implementing web application firewalls to detect and block malicious script injection attempts. The vulnerability aligns with CWE-79 which specifically addresses cross-site scripting flaws, and follows ATT&CK technique T1566.001 for initial access through spearphishing attachments, as the malicious scripts could be embedded in email content to target administrators. Network segmentation and principle of least privilege should be enforced to limit potential damage if exploitation occurs, and regular security audits should verify that no malicious scripts have been successfully injected into the system. Organizations should also consider implementing automated patch management systems to ensure timely deployment of security updates across all WordPress installations.