CVE-2026-33731

Description

## Summary The Authorize.Net webhook handler at `plugin/AuthorizeNet/webhook.php` contains a signature verification bypass that allows an attacker to forge webhook requests with arbitrary payment amounts and target user IDs. By supplying a valid transaction ID from a small legitimate purchase, the attacker bypasses signature validation and credits arbitrary wallet balances to any user account via attacker-controlled payload fields. ## Details Three flaws combine into an exploit chain: ### 1. Signature Bypass via OR Logic (webhook.php:33) ```php if (!$parsed['signatureValid'] && (empty($txnInfo) || !empty($txnInfo['error']))) { http_response_code(401); echo 'invalid signature'; exit; } ``` The webhook is rejected only when **both** conditions are true: the signature is invalid **AND** the transaction lookup fails. If the attacker supplies a real transaction ID (e.g., from their own $1 purchase), `getTransactionDetails()` succeeds and returns valid data, so the second condition is false. The invalid signature is silently ignored. ### 2. Payload Values Override API-Fetched Values (AuthorizeNet.php:169-171, webhook.php:44-48) In `analyzeTransactionFromWebhook()`, `users_id` and `amount` are extracted from the attacker-controlled webhook **payload** first: ```php $users_id = isset($metadata['users_id']) ? (int)$metadata['users_id'] : null; $amount = isset($payload['amount']) ? (float)$payload['amount'] : ...; ``` The fallback logic in webhook.php only applies when the analysis values are empty/falsy: ```php if (!$analysis['users_id'] && !empty($txnInfo['users_id'])) { $analysis['users_id'] = (int)$txnInfo['users_id']; } if (!$analysis['amount'] && isset($txnInfo['amount'])) { $analysis['amount'] = (float)$txnInfo['amount']; } ``` Since the forged payload already provides both values, the authoritative API-fetched values are never used. ### 3. Missing Approval Check (webhook.php:61-75) The code checks only that `users_id` and `amount` are non-empty before calling `processSinglePayment()`. The `isApproved` field is computed in `analyzeTransactionFromWebhook()` (line 222-228) but **never verified** before crediting the wallet at line 68-75. ## PoC **Prerequisites:** Attacker has a low-privileged account on the AVideo instance and has made at least one legitimate small Authorize.Net purchase (e.g., $1.00), noting the transaction ID (e.g., `60123456789`). 1. Immediately after the purchase completes (to race the legitimate webhook), send a forged webhook: ```bash curl -X POST https://target.com/plugin/AuthorizeNet/webhook.php \ -H 'Content-Type: application/json' \ -d '{ "eventType": "net.authorize.payment.authcapture.created", "payload": { "id": "60123456789", "amount": 99999.99, "responseCode": 1, "metadata": { "users_id": 2 } } }' ``` 2. The signature check fails (no `X-ANET-Signature` header), but `getTransactionDetails('60123456789')` succeeds because it is a real transaction. The OR condition on line 33 is not fully satisfied, so execution continues. 3. `analyzeTransactionFromWebhook()` uses the forged payload's `amount: 99999.99` and `metadata.users_id: 2`. 4. `processSinglePayment()` credits $99,999.99 to user ID 2's wallet via `addBalance()`. 5. The dedup key is `sha1('net.authorize.payment.authcapture.created' . '60123456789')`, so the legitimate webhook arriving later is silently discarded as a duplicate. 6. The attacker can repeat with new transaction IDs from additional small purchases for cumulative balance inflation. ## Impact - **Wallet balance inflation:** Attacker credits arbitrary amounts to any user's wallet without corresponding payment, bypassing the payment gateway's actual charge amount. - **Premium content access:** Inflated wallet balance allows purchasing all paid/premium video content without real payment. - **Subscription fraud:** By including `plans_id` in forged metadata, the attacker can activate premium subscriptions (webhook.php:86-134) without corresponding payment. - **Financial loss:** Platform owner loses revenue from fraudulently accessed premium content and services. ## Recommended Fix **1. Reject webhooks with invalid signatures unconditionally** — the transaction lookup should only be used for data enrichment *after* signature validation passes: ```php // webhook.php line 33 — FIX: reject on invalid signature alone if (!$parsed['signatureValid']) { _error_log('[Authorize.Net webhook] Bad signature'); http_response_code(401); echo 'invalid signature'; exit; } ``` **2. Use API-fetched values as authoritative** — in webhook.php lines 44-55, invert the precedence so `$txnInfo` values always override payload values: ```php // Always prefer API-fetched values over payload values if (!empty($txnInfo['users_id'])) { $analysis['users_id'] = (int)$txnInfo['users_id']; } if (isset($txnInfo['amount'])) { $analysis['amount'] = (float)$txnInfo['amount']; } ``` **3. Check `isApproved` before processing** — add a gate before `processSinglePayment()`: ```php if (!$analysis['isApproved']) { _error_log('[Authorize.Net webhook] Transaction not approved'); http_response_code(400); echo 'transaction not approved'; exit; } ```