The WhatsApp and Linear bot adapters verify the inbound webhook HMAC signature only when a secret is configured. When the secret environment variable is unset — the default on a fresh install and common in development — verification is skipped entirely and the webhook body is parsed and dispatched as a genuine, trusted event. A remote, unauthenticated attacker who can reach the bot's webhook endpoint can inject arbitrary platform events.

Affected code:

WhatsApp - src/praisonai/praisonai/bots/whatsapp.py

• init (line 108): self._app_secret = app_secret or os.environ.get("WHATSAPP_APP_SECRET", "") -> defaults to ""
• route (line 246): app.router.add_post(self._webhook_path, self._handle_webhook) -> default path "/webhook"
• _handle_webhook (lines 585-595): if self._app_secret: gates the ENTIRE check; when falsy the body is json.loads()'d and dispatched to _process_webhook_data() with no verification.

Linear - src/praisonai/praisonai/bots/linear.py

• init (line 86): self._signing_secret = signing_secret or os.environ.get("LINEAR_WEBHOOK_SECRET", "") -> ""
• _handle_webhook (lines 244-248): same if self._signing_secret: fail-open guard.
• start() (lines 169-170): only logs a warning; does not fail closed.

The _verify_signature implementations themselves are correct (constant-time HMAC-SHA256); the defect is that verification is bypassed when the secret is absent.

Impact:

• WhatsApp: attacker POSTs a crafted Meta Cloud API payload spoofing any sender and message text; injected into agent sessions and processed as a real user message (prompt injection, unauthorized agent/command invocation, contact impersonation).
• Linear: attacker POSTs forged AgentSession / Comment events, causing the agent to act on and comment on issues no legitimate event referenced. The webhook routes require no other authentication, so exploitation needs only network reachability.

Proof of concept (bot started without the secret - the default):

curl -X POST http://VICTIM:PORT/webhook
-H 'Content-Type: application/json'
-d '{"object":"whatsapp_business_account","entry":[{"changes":[{"value": {"messages":[{"from":"15551234567","id":"wamid.x","type":"text", "text":{"body":"attacker-injected message"}}]}}]}]}'

No X-Hub-Signature-256 header; bot returns 200 and processes the message.

Linear: omit LINEAR_WEBHOOK_SECRET and POST without a Linear-Signature header.

A self-contained PoC that executes the real _handle_webhook / _verify_signature source extracted from the repo confirms: secret unset -> status 200, payload dispatched (VULNERABLE); secret set + no signature -> status 403, nothing dispatched (control).