RustChain Webhook Verification Bypass Patched: Default-Deny Policy Replaces Dangerous Default-Allow

A security vulnerability in the RustChain ecosystem's webhook verification system has been patched after researchers identified a critical flaw in signature validation logic. The issue, tracked as GitHub issue #4995, allowed webhook signature verification to be bypassed entirely when the WEBHOOK_SECRET environment variable was not configured. In affected deployments, the `verify_webhook_signature` function returned `True` by default when no secret was present, effectively disabling all signature checks for incoming GitHub webhook events.

The vulnerability exposed unconfigured deployments to potential abuse. Without signature verification, anyone could forge GitHub webhook payloads and send them directly to affected systems. This raised the risk of triggering unintended bounty payments or tip bot actions for non-existent events. The flaw represented a departure from modern security architecture principles, which favor default-deny configurations over default-allow behavior. The fix replaces the permissive logic with a default-deny approach: when no secret is configured, the verification function now returns `False` and logs a warning, consistent with the RustChain ecosystem's ongoing migration toward stricter authentication patterns.

The patch has been validated through updated test cases. The test `test_no_secret_configured_rejects_all` now expects the verification function to return `False` when no secret is present, and the updated test suite passes successfully. Developers who maintain RustChain integrations should verify their webhook configurations include a properly set WEBHOOK_SECRET to ensure signature verification remains active. The finding underscores the importance of explicit configuration requirements for security-sensitive webhook handlers, where the absence of a credential should never equate to disabling protections.