CVE-2026-77999: j2commerce.com j2store Extension For Joomla

High severity, CVSS 8.7. EPSS: 0.4% chance of exploitation in the next 30 days.

Joomla Extension - j2commerce.com - Unauthenticated PayPal callback forgery leading to order confirmation fraud in J2Store 1.0.0-3.3.21, 4.0.0-4.0.21, 4.1.0-4.1.6 - The PayPal IPN listener's signature check (`_validateIPN()`) accepted `UNVERIFIED` and any non-`INVALID` response as valid, made its verification request with `CURLOPT_SSL_VERIFYPEER` disabled, and stored its verdict in a field nothing downstream ever checked — so processing continued regardless of the outcome. Separately, the paid-amount comparison only ran when `mc_gross` was a positive number; omitting the field from the POST body (`floatval(null) == 0`) skipped the check entirely. Combined with a merchant-configured `receiver_email` and a sequential, enumerable order id read from the `custom` field, an anonymous POST was enough to move a pending order straight to `CONFIRMED` with no payment, or force another customer's pending order to `FAILED`. `paypalv2.php` performed no amount check under any circumstances.

Affected products

• j2commerce.com j2store Extension For Joomla: version 1.0.0-3.3.21 only; version 4.0.0-4.0.21 only; version 4.1.0-4.1.6 only

Published 2026-09-03. Last modified 2026-09-03.