Attack Chain

1. Attacker Reconnaissance: An attacker identifies a target application utilizing pytonapi with TonapiWebhookDispatcher configured to use a custom webhook path (e.g., /hook/custom).
2. Payload Crafting: The attacker constructs a malicious JSON payload designed to mimic a legitimate pytonapi webhook event (e.g., an account_tx notification) but containing forged data (e.g., a FORGED_TX_HASH).
3. Exploitation Attempt: The attacker sends an unauthenticated HTTP POST request to the application's custom webhook endpoint (e.g., https://victim.example/hook/custom), embedding the forged JSON payload in the request body. The Authorization header is either omitted or contains an incorrect bearer token.
4. Vulnerability Trigger: The pytonapi TonapiWebhookDispatcher instance receives the incoming HTTP request. When processing the request for the custom path, the dispatcher attempts to retrieve an expected_token from its internal map using self._tokens.get(path).
5. Authentication Bypass: Because custom paths are never registered in _tokens, the expected_token variable becomes None. This causes the subsequent authentication check if expected_token is not None to evaluate to False, silently bypassing the entire authentication mechanism.
6. Payload Processing: The dispatcher proceeds to parse the attacker's forged JSON payload as if it were a legitimate and authenticated webhook event.
7. Impact Delivery: The victim-defined asynchronous event handler (e.g., on_custom_tx) associated with the custom path is invoked by the dispatcher, receiving and processing the attacker-controlled forged data.
8. Adverse Action: The victim's application executes its business logic (e.g., updating account balances, initiating payments, dispatching notifications) based on the attacker's forged information, leading to financial loss, data corruption, or other integrity compromises.

Impact

This vulnerability, classified as Improper Authentication (CWE-287), critically impacts the integrity of applications using pytonapi version 2.2.0 that have registered webhook handlers with the path= argument. There is no specific number of victims or sectors identified, but any application meeting these criteria is fully exposed. A successful exploitation allows an unauthenticated remote attacker to inject arbitrary, forged TON blockchain event data, directly triggering and manipulating victim-defined business logic. This can lead to severe consequences such as fraudulent payment processing, incorrect account state updates, or the dispatch of misleading notifications, resulting in financial losses or operational disruption. Confidentiality is not directly affected, but data integrity and the reliability of automated processes are significantly compromised.

Recommendation

• Update pytonapi to a patched version greater than 2.2.0 to resolve the GHSA-3fcr-jvgp-7f58 authentication bypass.
• Deploy the Sigma rule "Detect Successful POST to pytonapi Custom Webhook Path (GHSA-3fcr-jvgp-7f58)" to your SIEM solution to identify potential exploitation attempts against vulnerable pytonapi applications.
• Review webserver access logs for webserver entries indicating successful (HTTP 200 OK) POST requests to custom webhook paths (e.g., /hook/custom) that lack expected authentication headers or originate from unexpected sources.