# CVE-2026-77999: J2Store PayPal IPN signature bypass and order confirmation fraud

Source: https://junglewise.ai/threats/cve-2026-77999-j2store-paypal-ipn-signature-bypass-and-order-confirmation-fraud  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-03. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-77999 · Severity: info · CVSS 9.1 · Published 2026-09-03

J2Store is a popular Joomla eCommerce extension that processes online payments. An attacker can forge PayPal payment notifications to confirm orders without payment, or sabotage other customers' orders by marking them as failed. This could allow fraudsters to obtain products or services for free, and disrupt legitimate customers' purchases.

Technologies: [J2commerce.Com J2Store](https://junglewise.ai/threats/technologies/j2store). Vendors: [J2commerce.Com](https://junglewise.ai/threats/vendors/j2commerce-com).

## Quick answers

**Is CVE-2026-77999 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-77999 being exploited in the wild.

**How severe is CVE-2026-77999?** Informational severity, with a CVSS score of 9.1, published 3 September 2026.

**Which products and versions are affected?** J2commerce.Com J2Store 1.0.0-3.3.21, 4.0.0-4.0.21, 4.1.0-4.1.6.

**Is there a fix for CVE-2026-77999?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-77999 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-77999?** Check whether you run J2commerce.Com J2Store at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability exists in the PayPal IPN (Instant Payment Notification) listener's verification logic. The `_validateIPN()` function accepts `UNVERIFIED` responses and any non-`INVALID` result as valid, making SSL verification requests with `CURLOPT_SSL_VERIFYPEER` disabled, and storing the verdict in an unused field that downstream processing never checks. Additionally, the paid-amount comparison only executes when `mc_gross` is positive; omitting the field bypasses the check entirely via `floatval(null) == 0`. Combined with an enumerable sequential order ID and the merchant-configured receiver email, an unauthenticated attacker can POST a forged IPN to move a pending order to `CONFIRMED` status with no actual payment, or force another customer's order to `FAILED` status. The PayPal v2 plugin (`paypalv2.php`) performs no amount verification under any circumstances. No authentication is required; the attack is network-accessible.

## Affected products

- j2commerce.com J2Store 1.0.0-3.3.21, 4.0.0-4.0.21, 4.1.0-4.1.6

## Timeline

- 2026-09-03: disclosed

## References

- [https://www.j2commerce.com/](https://www.j2commerce.com/)

## Related threats

- [J2Store PayPal parameter injection in redirect](https://junglewise.ai/threats/cve-2026-82191-j2store-paypal-parameter-injection-in-redirect)
- [J2Store order status manipulation via unauthenticated request](https://junglewise.ai/threats/cve-2026-82189-j2store-order-status-manipulation-via-unauthenticated-request)
- [J2Store SQL injection in storefront product list](https://junglewise.ai/threats/cve-2026-81567-j2store-sql-injection-in-storefront-product-list)
- [J2Commerce J2Store missing CSRF protection in checkout controllers](https://junglewise.ai/threats/cve-2026-78081-j2commerce-j2store-missing-csrf-protection-in-checkout)
- [J2Store missing authorization in Apps controller](https://junglewise.ai/threats/cve-2026-78069-j2store-missing-authorization-in-apps-controller)