j2commerce J2Store Extension up to 4.1.6 PayPal IPN Listener paypalv2.php _validateIPN custom authorization

Summaryinfo

A vulnerability has been found in j2commerce J2Store Extension up to 4.1.6 and classified as problematic. This vulnerability affects the function _validateIPN of the file paypalv2.php of the component PayPal IPN Listener. This manipulation of the argument custom causes authorization. This vulnerability is handled as CVE-2026-77999. The attack can be initiated remotely. There is not any exploit available.

Detailsinfo

A vulnerability was found in j2commerce J2Store Extension up to 4.1.6. It has been declared as problematic. Affected by this vulnerability is the function _validateIPN of the file paypalv2.php of the component PayPal IPN Listener. The manipulation of the argument custom with an unknown input leads to a authorization vulnerability. The CWE definition for the vulnerability is CWE-862. The product does not perform an authorization check when an actor attempts to access a resource or perform an action. As an impact it is known to affect integrity. The summary by CVE is:

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.

The advisory is shared at j2commerce.com. This vulnerability is known as CVE-2026-77999 since 08/21/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 09/03/2026).

By approaching the search of inurl:paypalv2.php it is possible to find vulnerable targets with Google Hacking.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Vendor

• j2commerce

Name

• J2Store Extension

Version

• 1.0
• 3.3.0
• 3.3.1
• 3.3.2
• 3.3.3
• 3.3.4
• 3.3.5
• 3.3.6
• 3.3.7
• 3.3.8
• 3.3.9
• 3.3.10
• 3.3.11
• 3.3.12
• 3.3.13
• 3.3.14
• 3.3.15
• 3.3.16
• 3.3.17
• 3.3.18
• 3.3.19
• 3.3.20
• 3.3.21
• 4.0
• 4.0.0
• 4.0.1
• 4.0.2
• 4.0.3
• 4.0.4
• 4.0.5
• 4.0.6
• 4.0.7
• 4.0.8
• 4.0.9
• 4.0.10
• 4.0.11
• 4.0.12
• 4.0.13
• 4.0.14
• 4.0.15
• 4.0.16
• 4.0.17
• 4.0.18
• 4.0.19
• 4.0.20
• 4.0.21
• 4.1.0
• 4.1.1
• 4.1.2
• 4.1.3
• 4.1.4
• 4.1.5
• 4.1.6

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CPE 2.2info

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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