CVE-2026-44826

Executive Summary

CVE-2026-44826 is an input validation vulnerability in Vvveb CMS, a PHP-based content management system with a page builder. The vulnerability resides in the cart-add endpoint, where the quantity parameter is not validated for negative values. An unauthenticated attacker can submit a negative integer as the quantity, which the server accepts and propagates through all downstream computations, including line totals, subtotals, taxes, and the grand total. This results in a negative total order being created in the merchant's database, displayed in the customer-facing cart UI, and processed through the checkout flow. The vulnerability is classified as a business logic flaw with a CVSS score of 7.5 (High), primarily due to the integrity impact on the merchant's order management system. No public exploit code or proof-of-concept is currently available, and the patch status is confirmed as fixed in version 1.0.8.2.

Supply Chain & Package Security

Vvveb CMS is a PHP application distributed via GitHub and its official website. The vulnerability is not related to a package manager (NPM, PyPI, Go, Ruby) but is a direct code-level flaw in the core application. Organizations using Vvveb CMS should verify their version and update to 1.0.8.2 or later. No supply chain compromise has been identified.

CVSS Breakdown & Threat Level

• CVSS Score: 7.5 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: None
• Integrity Impact: Low (negative order values)
• Availability Impact: None

The threat level is High due to the ease of exploitation (no authentication required) and the potential for financial and operational disruption. An attacker can create fraudulent orders that appear as "merchant owes customer" records, leading to accounting discrepancies, potential refund abuse, and loss of trust.

Deep Dive & Mechanics

The vulnerability is a classic input validation failure in the cart-add endpoint. The endpoint accepts a quantity parameter, which is expected to be a positive integer. However, the server does not validate the sign of the value. When a negative integer is submitted, it is stored and used in all subsequent calculations:

1. Line Total Calculation: line_total = price * quantity → becomes negative if quantity is negative.
2. Subtotal: Sum of all line totals → becomes negative.
3. Tax Calculation: tax = subtotal * tax_rate → becomes negative.
4. Grand Total: grand_total = subtotal + tax + shipping → becomes negative.

The customer-facing cart UI displays the negative grand total, and the checkout flow accepts it without validation. The order is then persisted in the database with a negative total. From the merchant's dashboard, this appears as a legitimate order with a negative total, which no normal workflow would produce.

The root cause is the lack of input validation on the quantity parameter. The fix in version 1.0.8.2 likely adds a check to ensure the quantity is a positive integer (e.g., if ($quantity <= 0) { // reject }).

Vulnerable vs. Patched Code

Vulnerable Code (prior to 1.0.8.2):

// cart-add endpoint
$quantity = $_POST['quantity']; // No validation
$product_id = $_POST['product_id'];
$price = getProductPrice($product_id);
$line_total = $price * $quantity; // Negative if quantity is negative
// ... further calculations

Patched Code (1.0.8.2):

// cart-add endpoint
$quantity = (int)$_POST['quantity'];
if ($quantity <= 0) {
    // Reject negative or zero quantity
    http_response_code(400);
    echo json_encode(['error' => 'Invalid quantity']);
    exit;
}
$product_id = $_POST['product_id'];
$price = getProductPrice($product_id);
$line_total = $price * $quantity;
// ... further calculations

The patch adds a simple check to ensure the quantity is greater than zero. This prevents negative values from being processed.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A running instance of Vvveb CMS version < 1.0.8.2.
• A product with a known price (e.g., $10.00).

Exploitation Steps:

1. Identify the cart-add endpoint (e.g., https://target.com/index.php?route=checkout/cart/add).
2. Send a POST request with a negative quantity:

   curl -X POST https://target.com/index.php?route=checkout/cart/add \
     -d "product_id=1&quantity=-5"
   

3. The server will accept the request and calculate a negative line total (e.g., -$50.00).
4. Proceed to checkout. The grand total will be negative.
5. Complete the order. The merchant's dashboard will show an order with a negative total.

Impact:

• The merchant sees a "negative order" that appears as if they owe the customer money.
• This can be used for accounting fraud, refund abuse, or to disrupt the merchant's financial records.

Blue Team

Detection:

• Monitor for POST requests to cart-add with negative or non-integer quantity values.
• Look for orders with negative totals in the database.
• Alert on any order where total < 0.

Prevention:

• Apply the patch by updating to Vvveb CMS 1.0.8.2.
• Implement a Web Application Firewall (WAF) rule to block requests with negative quantity values.
• Add server-side validation to ensure quantity is a positive integer.

Indicators of Compromise (IOCs)

• Network IOCs:

  • POST requests to /index.php?route=checkout/cart/add with quantity parameter containing negative integers.
  • HTTP responses with status 200 and negative total values in the JSON/HTML response.

• File IOCs:

  • Log entries in access.log showing requests with negative quantity values.
  • Database entries in the orders table with negative total column values.

• Behavioral IOCs:

  • Orders with negative totals appearing in the merchant dashboard.
  • Customer accounts with negative balance or credit.

Detection Engineering

YARA Rule

rule CVE_2026_44826_Vvveb_Negative_Quantity {
    meta:
        description = "Detects negative quantity parameter in Vvveb CMS cart-add requests"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "CVE-2026-44826"
        severity = "high"
    strings:
        $quantity_param = "quantity=" nocase
        $negative_value = /quantity=-\d+/ nocase
    condition:
        $quantity_param and $negative_value
}

Sigma Rule

title: Vvveb CMS Negative Quantity Exploitation
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects attempts to exploit CVE-2026-44826 by submitting negative quantity values to the cart-add endpoint.
author: Valters IT
date: 2026-01-01
logsource:
    category: webserver
    product: apache
    service: access_log
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'route=checkout/cart/add'
        cs-uri-query|re: 'quantity=-\d+'
    condition: selection
falsepositives:
    - Legitimate negative values are not expected in normal operation.
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2026-44826 Vvveb CMS Negative Quantity Exploitation";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"route=checkout/cart/add"; http_uri;
    pcre:"/quantity=-\d+/Ui";
    sid:1000001;
    rev:1;
    priority:1;
    reference:cve,2026-44826;
    classtype:attempted-recon;
)

Remediation & Mitigation

Immediate Actions:

1. Update Vvveb CMS to version 1.0.8.2 or later. This is the only confirmed fix.
2. Apply a WAF rule to block requests with negative quantity values:

   # Apache .htaccess example
   RewriteEngine On
   RewriteCond %{QUERY_STRING} quantity=-\d+ [NC]
   RewriteRule ^ - [F,L]
   

3. Review existing orders in the database for negative totals and investigate any anomalies.

Long-term Mitigations:

• Implement input validation on all user-supplied parameters, especially numeric ones.
• Use parameterized queries or prepared statements to prevent SQL injection (though not directly related, it's good practice).
• Conduct regular security audits and penetration testing.
• Monitor for unusual order patterns, such as negative totals or extremely low totals.

Valters IT Signature: This report was generated by Valters IT DevSecOps & CTI Division. For further analysis or incident response support, contact your Valters IT representative.