CVE-2025-13239

Executive Summary

CVE-2025-13239 is a security vulnerability in the Bdtask/CodeCanyon Isshue Multi Store eCommerce Shopping Cart Solution version 5. The flaw resides in the /submit_checkout endpoint, where the order_total_amount and cart_total_amount parameters can be manipulated to bypass the intended payment workflow. This allows an attacker to enforce a behavioral workflow, potentially completing a purchase without proper payment validation. The CVSS score is 4.3 (Medium), and the exploit has been publicly disclosed. The vendor has not responded to disclosure attempts, and no patch is currently available.

Note: This is a commercial PHP-based eCommerce solution, not a WordPress plugin. The vulnerability is in the application's own checkout logic.

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): None (N) - No user action required.
• Scope (S): Unchanged (U) - Impact is confined to the vulnerable component.
• Confidentiality (C): None (N) - No data exposure.
• Integrity (I): Low (L) - Payment workflow can be bypassed, leading to unauthorized order completion.
• Availability (A): None (N) - No denial of service.

Threat Level: Medium. The exploit is trivial to execute and requires no authentication, but the direct impact is limited to workflow bypass (e.g., placing orders without payment). However, this could lead to financial loss or inventory manipulation.

Deep Dive & Mechanics

The vulnerability is a Behavioral Workflow Enforcement Bypass (CWE-841). The /submit_checkout endpoint processes order submission. The application likely validates the total amount against a server-side calculation or session data. However, the parameters order_total_amount and cart_total_amount are accepted from the client-side request without proper server-side re-validation.

An attacker can intercept the POST request to /submit_checkout and modify these parameters to a lower value (e.g., 0.01 or 0.00). The application then processes the order as if the correct amount was paid, bypassing the payment gateway integration. This is a classic case of trusting client-side input for critical financial operations.

Attack Flow:

1. Attacker adds items to cart and proceeds to checkout.
2. Attacker intercepts the POST request to /submit_checkout.
3. Attacker modifies order_total_amount and/or cart_total_amount to a minimal value.
4. The server processes the order, marking it as paid/completed.
5. Attacker receives the order confirmation without actual payment.

Vulnerable vs. Patched Code

Since no patch is available, we can only infer the vulnerable pattern. The vulnerable code likely resembles:

// Vulnerable: Directly uses POST parameter without server-side validation
$totalAmount = $_POST['order_total_amount'];
// Process order with $totalAmount

A patched version would:

// Patched: Recalculate total from server-side cart data
$cartTotal = calculateCartTotalFromSession();
if ($_POST['order_total_amount'] != $cartTotal) {
    die("Invalid total amount");
}
// Process order with $cartTotal

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Target running Isshue Multi Store v5.
• Network access to the /submit_checkout endpoint.

Exploit Steps:

1. Add items to cart and initiate checkout.
2. Use a proxy (e.g., Burp Suite) to intercept the POST request to /submit_checkout.
3. Modify the parameters:
   • order_total_amount=0.01
   • cart_total_amount=0.01
4. Forward the request.
5. Verify order is placed without payment.

Example cURL command:

curl -X POST https://target.com/submit_checkout \
  -d "order_total_amount=0.01&cart_total_amount=0.01&other_params=..."

Blue Team (Detection & Hardening)

Detection:

• Monitor for POST requests to /submit_checkout with order_total_amount or cart_total_amount values that do not match the expected cart total.
• Alert on multiple rapid checkout attempts with varying amounts.

Hardening (until patch):

• Implement server-side total recalculation from session/cart data.
• Validate that the submitted total matches the server-calculated total.
• Add CSRF tokens to the checkout form.
• Log all checkout attempts with submitted amounts for auditing.

Indicators of Compromise (IOCs)

• Network: POST requests to /submit_checkout with anomalous order_total_amount or cart_total_amount values (e.g., 0.01, 0.00, negative numbers).
• Logs: Order records where total_amount is significantly lower than the sum of item prices.
• Application: Orders marked as "paid" or "completed" without corresponding payment gateway transaction IDs.

Detection Engineering

YARA Rule

rule CVE_2025_13239_Checkout_Bypass {
    meta:
        description = "Detects exploitation attempts of CVE-2025-13239 in Isshue Multi Store"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-13239"
    strings:
        $submit_checkout = "/submit_checkout"
        $order_total = "order_total_amount"
        $cart_total = "cart_total_amount"
        $low_amount = /order_total_amount=[0-9]+\.[0-9]{2}/  // Matches any decimal amount
    condition:
        $submit_checkout and ($order_total or $cart_total) and $low_amount
}

Sigma Rule

title: CVE-2025-13239 Checkout Amount Manipulation
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects manipulation of order_total_amount or cart_total_amount in POST requests to /submit_checkout
author: Valters IT
date: 2025/04/10
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-method: POST
        cs-uri-stem: "/submit_checkout"
    keywords:
        - "order_total_amount"
        - "cart_total_amount"
    condition: selection and keywords
falsepositives:
    - Legitimate checkout requests with correct amounts
level: medium

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-13239 - Isshue Checkout Amount Manipulation";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/submit_checkout"; http_uri;
    content:"order_total_amount"; http_client_body;
    pcre:"/order_total_amount=[0-9]+\.[0-9]{2}/";
    sid:10000001;
    rev:1;
    reference:cve,2025-13239;
    priority:2;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the checkout endpoint if possible until a patch is available.
2. Implement a Web Application Firewall (WAF) rule to block POST requests to /submit_checkout with modified amount parameters.
3. Audit all orders placed since the vulnerability was disclosed for fraudulent transactions.

Long-term Fix:

• The vendor must implement server-side validation of the total amount against the cart contents.
• Apply the principle of never trusting client-side input for financial calculations.
• Consider using signed or encrypted tokens for checkout data.

Workaround:

• Modify the application code to recalculate the total on the server before processing the order. If you have access to the source code, add:

$serverTotal = calculateTotalFromCart();
if ($_POST['order_total_amount'] != $serverTotal) {
    header('HTTP/1.1 400 Bad Request');
    die('Invalid total amount');
}

Valters IT
Securing Digital Frontiers