CVE-2018-25250: MyBB Profile Plugin XSS Vulnerability

CVE-2018-25250 Overview

CVE-2018-25250 is a persistent Cross-Site Scripting (XSS) vulnerability affecting MyBB Last User's Threads in Profile Plugin version 1.2. This vulnerability allows attackers to inject malicious scripts by crafting thread subjects with script tags. When users visit an attacker's profile page, any malicious JavaScript payload embedded in thread subjects will execute in the context of the victim's browser session.

Critical Impact

Attackers can execute arbitrary JavaScript in victims' browsers, potentially leading to session hijacking, credential theft, or malicious actions performed on behalf of authenticated users.

Affected Products

• MyBB Last User's Threads in Profile Plugin version 1.2

Discovery Timeline

• 2026-04-04 - CVE CVE-2018-25250 published to NVD
• 2026-04-07 - Last updated in NVD database

Technical Details for CVE-2018-25250

Vulnerability Analysis

This persistent XSS vulnerability (CWE-79) exists within the MyBB Last User's Threads in Profile Plugin due to insufficient input sanitization when processing thread subject fields. When the plugin renders a user's recent threads on their profile page, it fails to properly escape or validate the content of thread subjects before inserting them into the HTML output.

The vulnerability is exploitable over the network and requires low privileges (authenticated forum user) along with some user interaction (victim must visit the attacker's profile page). This makes it a stored XSS attack where the malicious payload persists in the database and executes whenever the affected page is loaded.

Root Cause

The root cause is improper input validation and output encoding in the plugin's thread subject handling. When displaying a user's recent threads on their profile, the plugin directly outputs thread subject content without applying HTML entity encoding or sanitizing potentially dangerous characters like <, >, and ". This allows attackers to inject raw HTML and JavaScript that the browser interprets as legitimate code.

Attack Vector

The attack vector involves a malicious authenticated user creating a new forum thread with a crafted subject containing JavaScript code. When the plugin renders the attacker's profile page to display their recent threads, the malicious script embedded in the thread subject executes in the browser of any user viewing that profile.

The attack workflow involves creating a thread with a subject containing script tags and payload code. When any user navigates to the attacker's profile page, the plugin fetches the attacker's recent threads and renders them without proper sanitization, causing the injected JavaScript to execute in the victim's browser context. For detailed exploitation techniques, refer to the Exploit-DB #44339 entry.

Detection Methods for CVE-2018-25250

Indicators of Compromise

• Thread subjects containing HTML script tags or JavaScript event handlers such as <script>, onerror=, onload=, or onclick=
• Unusual forum thread subjects with encoded characters or obfuscated JavaScript code
• User reports of unexpected browser behavior or redirects when viewing certain user profiles

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block XSS payloads in HTTP request parameters
• Enable server-side logging of all thread creation and modification events for forensic analysis
• Deploy browser-based XSS auditors or Content Security Policy (CSP) headers to prevent inline script execution

Monitoring Recommendations

• Monitor database entries for thread subjects containing suspicious patterns like <script or JavaScript URI schemes
• Review web server access logs for repeated profile page requests that may indicate XSS payload testing
• Configure alerting for Content Security Policy violations which may indicate attempted XSS exploitation

How to Mitigate CVE-2018-25250

Immediate Actions Required

• Disable the MyBB Last User's Threads in Profile Plugin until a patched version is available
• Review existing thread subjects in the database for any injected malicious content
• Implement Content Security Policy (CSP) headers to mitigate the impact of any successful XSS attacks
• Educate users about the risk and advise against visiting untrusted user profiles

Patch Information

Review the MyBB Mod Overview page for any updated versions or patches released by the plugin author. Additionally, consult the VulnCheck Advisory for MyBB for the latest security guidance and patch availability information.

Workarounds

• Disable or uninstall the vulnerable plugin from MyBB installations
• Implement server-side input validation to strip HTML tags from thread subjects before storage
• Apply output encoding using htmlspecialchars() or equivalent functions when rendering thread subjects
• Deploy Content Security Policy headers with strict script-src directives to block inline script execution

# Configuration example - Add to MyBB global.php or plugin file
# Implement output encoding for thread subjects
$sanitized_subject = htmlspecialchars($thread['subject'], ENT_QUOTES, 'UTF-8');