CVE-2026-3641: The Appmax plugin for WordPress is vulnerable to Improper Input Validation in all versions up to, and including, 1.0.3. This is due to the plugin regi...

Description

The Appmax plugin for WordPress is vulnerable to Improper Input Validation in all versions up to, and including, 1.0.3. This is due to the plugin registering a public REST API webhook endpoint at /webhook-system without implementing webhook signature validation, secret verification, or any mechanism to authenticate that incoming webhook requests genuinely originate from the legitimate Appmax payment service. The plugin directly processes untrusted attacker-controlled input from the 'event' and 'data' parameters without verifying the webhook's authenticity. This makes it possible for unauthenticated attackers to craft malicious webhook payloads that can modify the status of existing WooCommerce orders (e.g., changing them to processing, refunded, cancelled, or pending), create entirely new WooCommerce orders with arbitrary data, create new WooCommerce products with attacker-controlled names/descriptions/prices, and write arbitrary values to order post metadata by spoofing legitimate webhook events.

Metrics

CVSS 3.1

5.3/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS Probability

0.30%

21.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-20

References

Timeline

Published: Mar 21, 2026
Last Modified: Jun 17, 2026
Status: Deferred

Frequently Asked Questions

What is CVE-2026-3641?

The Appmax plugin for WordPress is vulnerable to Improper Input Validation in all versions up to, and including, 1.0.3. This is due to the plugin registering a public REST API webhook endpoint at /webhook-system without implementing webhook signature validation, secret verification, or any mechanism to authenticate that incoming webhook requests genuinely originate from the legitimate Appmax payment service. The plugin directly processes untrusted attacker-controlled input from the 'event' and 'data' parameters without verifying the webhook's authenticity. This makes it possible for unauthenticated attackers to craft malicious webhook payloads that can modify the status of existing WooCommerce orders (e.g., changing them to processing, refunded, cancelled, or pending), create entirely new WooCommerce orders with arbitrary data, create new WooCommerce products with attacker-controlled names/descriptions/prices, and write arbitrary values to order post metadata by spoofing legitimate webhook events.

How severe is CVE-2026-3641?

CVE-2026-3641 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 0.30% probability of exploitation in the next 30 days.

How do I fix CVE-2026-3641?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.