CVE-2026-3641
Unauthenticated Input Validation Flaw in Appmax WordPress Plugin
Publication date: 2026-03-21
Last updated on: 2026-03-21
Assigner: Wordfence
Description
Description
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| appmax | plugin | to 1.0.3 (inc) |
| appmax | appmax_plugin | to 1.0.3 (inc) |
Helpful Resources
Exploitability
| CWE ID | Description |
|---|---|
| CWE-20 | The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. |
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?
The Appmax plugin for WordPress has a vulnerability due to improper input validation in all versions up to and including 1.0.3. The plugin registers a public REST API webhook endpoint at /webhook-system but does not implement any webhook signature validation, secret verification, or authentication mechanisms to confirm that incoming webhook requests are from the legitimate Appmax payment service.
Because of this, unauthenticated attackers can send malicious webhook payloads with attacker-controlled 'event' and 'data' parameters. The plugin processes these inputs without verifying their authenticity, allowing attackers to manipulate WooCommerce orders and products.
- Modify the status of existing WooCommerce orders (e.g., changing them to processing, refunded, cancelled, or pending).
- Create new WooCommerce orders with arbitrary data.
- Create new WooCommerce products with attacker-controlled names, descriptions, and prices.
- Write arbitrary values to order post metadata by spoofing legitimate webhook events.
How can this vulnerability impact me? :
This vulnerability can allow attackers to manipulate your WooCommerce store by changing order statuses, creating fraudulent orders, adding malicious or misleading products, and altering order metadata. Such actions can disrupt business operations, cause financial loss, damage customer trust, and potentially lead to fraudulent transactions.
How does this vulnerability affect compliance with common standards and regulations (like GDPR, HIPAA)?:
I don't know
How can this vulnerability be detected on my network or system? Can you suggest some commands?
Detection of this vulnerability involves identifying the presence of the Appmax plugin for WordPress, specifically versions up to and including 1.0.3, and monitoring for unauthenticated requests to the /webhook-system REST API endpoint.
Since the plugin does not implement webhook signature validation or secret verification, any incoming HTTP requests to /webhook-system that modify WooCommerce orders or products without proper authentication could indicate exploitation attempts.
You can use network monitoring or web server logs to detect suspicious POST requests to the /webhook-system endpoint.
- Use curl or similar tools to test the endpoint: curl -X POST https://yourwordpresssite.com/webhook-system -d 'event=test&data=test'
- Check web server access logs for POST requests to /webhook-system from unknown or suspicious IP addresses.
- Use WordPress CLI or plugin management commands to verify the installed version of the Appmax plugin.
What immediate steps should I take to mitigate this vulnerability?
Immediate mitigation steps include disabling or updating the Appmax plugin to a version that addresses the vulnerability if available.
If an update is not available, restrict access to the /webhook-system endpoint by implementing authentication mechanisms such as IP whitelisting, firewall rules, or web application firewall (WAF) rules to block unauthorized requests.
Monitor WooCommerce orders and products for unauthorized changes and review logs for suspicious activity.
Consider temporarily disabling the webhook functionality until a secure fix is applied.