fix(lark): verify webhook event-subscription signature before dispatch

The Lark/Feishu webhook handler (both the current lark-omni adapter and
the legacy lark adapter) parsed and dispatched inbound HTTP callback
events without checking Lark's own X-Lark-Signature header, and the
Encrypt Key config field used to decrypt payloads is optional and empty
by default. Any caller who reached a bot's webhook URL could inject
fabricated message/card-action events with an attacker-chosen sender,
chat, and content.

Add signature verification matching Lark's documented
event-security-verification scheme (sha256 of timestamp + nonce +
encrypt_key + body, compared to X-Lark-Signature) to both
implementations, rejecting any callback that lacks a valid signature or
whose bot has no Encrypt Key configured. Adds regression tests covering
the rejection paths and updates the two existing webhook tests to
present a valid signature.

src/langbot/pkg/platform/adapters/lark/adapter.py

@@ -9,6 +9,7 @@ import threading
 import asyncio
 import base64
 import hashlib
+import hmac
 import json
 import time
 import traceback
@@ -629,9 +630,34 @@ class LarkAdapter(LarkAPIMixin, abstract_platform_adapter.AbstractPlatformAdapte
             return f'{event.group.id}_{thread_id}'
         return None
 
+    def _verify_webhook_signature(self, request, raw_body: bytes) -> bool:
+        """Verify the Lark/Feishu event-subscription callback signature.
+
+        Per Lark's own event-security-verification protocol, a callback is
+        authentic only if its ``X-Lark-Signature`` header equals
+        sha256(timestamp + nonce + encrypt_key + body). Without this check
+        any caller who reaches this webhook path can inject fabricated
+        events (spoofed messages, card actions) regardless of whether they
+        hold the app's Encrypt Key.
+        """
+        encrypt_key = self.config.get('encrypt-key', '') or ''
+        if not encrypt_key:
+            return False
+        timestamp = request.headers.get('X-Lark-Request-Timestamp', '')
+        nonce = request.headers.get('X-Lark-Request-Nonce', '')
+        signature = request.headers.get('X-Lark-Signature', '')
+        if not timestamp or not nonce or not signature:
+            return False
+        expected = hashlib.sha256((timestamp + nonce + encrypt_key).encode('utf-8') + raw_body).hexdigest()
+        return hmac.compare_digest(expected, signature)
+
     async def handle_unified_webhook(self, bot_uuid: str, path: str, request):
         try:
-            data = await request.json
+            raw_body = await request.get_data()
+            if not self._verify_webhook_signature(request, raw_body):
+                await self.logger.error('Lark webhook signature verification failed, rejecting callback')
+                return {'code': 403, 'message': 'signature verification failed'}, 403
+            data = json.loads(raw_body)
             if 'encrypt' in data:
                 data = json.loads(self.cipher.decrypt_string(data['encrypt']))
             event_type = self.get_event_type(data)

src/langbot/pkg/platform/sources/lark.py

@@ -5,6 +5,7 @@ from lark_oapi.api.im.v1 import CreateImageRequest, CreateImageRequestBody, Crea
 import traceback
 import typing
 import asyncio
+import hmac
 import re
 import base64
 import uuid
@@ -2973,6 +2974,27 @@ class LarkAdapter(abstract_platform_adapter.AbstractMessagePlatformAdapter):
         else:
             return data['type']
 
+    def _verify_webhook_signature(self, request, raw_body: bytes) -> bool:
+        """Verify the Lark/Feishu event-subscription callback signature.
+
+        Per Lark's event-security-verification protocol, a callback is
+        authentic only if its ``X-Lark-Signature`` header equals
+        sha256(timestamp + nonce + encrypt_key + body). Without this check
+        any caller who reaches this webhook path can inject fabricated
+        events (spoofed messages, card actions) regardless of whether they
+        hold the app's Encrypt Key.
+        """
+        encrypt_key = self.config.get('encrypt-key', '') or ''
+        if not encrypt_key:
+            return False
+        timestamp = request.headers.get('X-Lark-Request-Timestamp', '')
+        nonce = request.headers.get('X-Lark-Request-Nonce', '')
+        signature = request.headers.get('X-Lark-Signature', '')
+        if not timestamp or not nonce or not signature:
+            return False
+        expected = hashlib.sha256((timestamp + nonce + encrypt_key).encode('utf-8') + raw_body).hexdigest()
+        return hmac.compare_digest(expected, signature)
+
     async def handle_unified_webhook(self, bot_uuid: str, path: str, request):
         """处理统一 webhook 请求。
         Args:
@@ -2983,7 +3005,11 @@ class LarkAdapter(abstract_platform_adapter.AbstractMessagePlatformAdapter):
             响应数据
         """
         try:
-            data = await request.json
+            raw_body = await request.get_data()
+            if not self._verify_webhook_signature(request, raw_body):
+                await self.logger.error('Lark webhook signature verification failed, rejecting callback')
+                return {'code': 403, 'message': 'signature verification failed'}, 403
+            data = json.loads(raw_body)
 
             if 'encrypt' in data:
                 encrypted = data['encrypt']
@@ -2991,7 +3017,6 @@ class LarkAdapter(abstract_platform_adapter.AbstractMessagePlatformAdapter):
             type = self.get_event_type(data)
             context = EventContext(data)
             if 'url_verification' == type:
-                # todo 验证verification token
                 return {'challenge': data.get('challenge')}
             elif 'app_ticket' == type:
                 self.app_ticket = context.event['app_ticket']