The package github.com/runatlantis/atlantis/server/controllers/events before 0.19.7 are vulnerable to Timing Attack in the webhook event validator code, which does not use a constant-time comparison function to validate the webhook secret. It can allow an attacker to recover this secret as an attacker and then forge webhook events.
https://github.com/runatlantis/atlantis/commit/48870911974adddaa4c99c8089e79b7d787fa820