CVE-2025-27354: Simple Email Subscriber XSS Vulnerability

CVE-2025-27354 Overview

CVE-2025-27354 is a reflected cross-site scripting (XSS) vulnerability in the Simple Email Subscriber WordPress plugin developed by phil88530. The flaw affects all plugin versions up to and including 2.3 and stems from improper neutralization of user-supplied input during web page generation [CWE-79]. An attacker can craft a malicious URL that, when clicked by a victim, executes arbitrary JavaScript in the victim's browser session. The vulnerability requires user interaction but no authentication, and the changed scope allows code execution in the context of the affected WordPress site.

Critical Impact
Successful exploitation enables session hijacking, credential theft, and administrative action takeover when a privileged WordPress user clicks a crafted link.

Affected Products

phil88530 Simple Email Subscriber WordPress plugin versions through 2.3
WordPress sites with simple-email-subscriber plugin installed and active
All deployments where the plugin processes unsanitized request parameters

Discovery Timeline

2025-04-17 - CVE-2025-27354 published to NVD
2026-04-23 - Last updated in NVD database

Technical Details for CVE-2025-27354

Vulnerability Analysis

The vulnerability is a reflected XSS issue in the Simple Email Subscriber plugin. The plugin reflects user-controllable request parameters into the rendered HTML response without applying proper output encoding or input sanitization. An attacker who lures a victim into clicking a crafted link triggers JavaScript execution in the victim's browser under the origin of the vulnerable WordPress site.

Because the issue is reflected, exploitation requires user interaction. However, the scope change indicates that injected scripts can affect resources beyond the vulnerable component, such as session cookies for the broader WordPress administrative interface. The EPSS data places exploitation probability in the moderate range relative to other published CVEs.

Root Cause

The plugin fails to apply WordPress sanitization functions such as esc_html(), esc_attr(), or sanitize_text_field() before echoing request data into HTML output. Input arrives via HTTP GET or POST parameters and is concatenated into the response page, allowing <script> payloads or HTML attribute breakouts to execute.

Attack Vector

Exploitation is network-based and requires no privileges. The attacker delivers a crafted URL through phishing, forum posts, or malicious advertising. When a logged-in WordPress administrator follows the link, the injected JavaScript executes with the administrator's session, enabling cookie theft, forced configuration changes, or creation of new administrative accounts. See the Patchstack XSS Vulnerability Advisory for additional technical context.

Detection Methods for CVE-2025-27354

Indicators of Compromise

Web server access logs containing requests to simple-email-subscriber endpoints with URL-encoded <script>, javascript:, or onerror= payloads in query strings
Unexpected WordPress administrator account creation or role escalation events following plugin-related requests
Outbound requests from administrator browsers to attacker-controlled domains immediately after visiting the WordPress admin panel

Detection Strategies

Inspect HTTP request and referrer logs for reflected payload patterns targeting plugin parameters
Deploy a Web Application Firewall (WAF) rule set with OWASP Core Rule Set XSS signatures applied to all /wp-content/plugins/simple-email-subscriber/ paths
Correlate browser-side Content Security Policy (CSP) violation reports with WordPress request logs to surface injection attempts

Monitoring Recommendations

Alert on administrator-initiated plugin or user changes that occur within seconds of an external referrer
Track plugin file integrity and changes to wp_users and wp_usermeta tables
Monitor email gateway and DNS resolution logs for phishing campaigns referencing the affected WordPress sites

How to Mitigate CVE-2025-27354

Immediate Actions Required

Deactivate and remove the Simple Email Subscriber plugin until a patched release is available, since the advisory lists all versions through 2.3 as vulnerable
Force WordPress administrator password resets and invalidate active sessions to revoke any tokens potentially exposed
Apply a WAF virtual patch that blocks request parameters containing HTML or script syntax for the plugin's endpoints

Patch Information

No fixed version is identified in the available advisory data. Defenders should monitor the Patchstack advisory and the WordPress.org plugin repository for an updated release beyond version 2.3.

Workarounds

Replace Simple Email Subscriber with an actively maintained subscription plugin that applies WordPress sanitization APIs
Enforce a strict Content Security Policy that disallows inline script execution on WordPress administrative pages
Restrict /wp-admin/ access by IP allowlist or VPN to reduce the population of administrators reachable by phishing links
Train administrators to avoid clicking unsolicited links that target the WordPress site domain

bash

# Example: disable the vulnerable plugin via WP-CLI
wp plugin deactivate simple-email-subscriber
wp plugin delete simple-email-subscriber

# Example: nginx rule to block obvious XSS payloads on plugin paths
# location ~* /wp-content/plugins/simple-email-subscriber/ {
#     if ($args ~* "(<|%3C)script") { return 403; }
# }