GHSA-jr9p-4h4j-6c58: Kimai: Default APP_SECRET in Docker Image Enables Cookie Forgery and Account Takeover

Summary The official Kimai Docker image ships with APP_SECRET=change_this_to_something_unique as the default environment variable. The Docker entrypoint does not override or validate this value. Any Kimai instance deployed using the Docker image without explicitly setting APP_SECRET runs with a publicly-known Symfony kernel.secret, enabling an unauthenticated attacker to forge HMAC-signed cookies and login links to take over any account including super_admin. Details Dockerfile:263 sets ENV APP_SECRET=change_this_to_something_unique. This value is consumed by config/packages/framework.yaml:7 as kernel.secret, which Symfony uses to HMAC-sign: - The KIMAI_REMEMBER remember-me cookie - LoginLink signatures - Password reset URLs - CSRF tokens The .docker/entrypoint.sh does not check for or replace the default sentinel value. The bare-metal .env.dist:38 ships the same default. No startup-time guard exists anywhere in the codebase that refuses to start when APP_SECRET equals the sentinel. User IDs are sequential integers starting from 1. The first super_admin account is almost always id=1. User IDs are visible in some URLs and API responses. *A PoC was provided, but removed for security reasons.* Impact Any Kimai instance deployed via the official Docker image without overriding APP_SECRET can be compromised from the internet. An unauthenticated attacker who can reach the Kimai URL can forge authentication tokens and log in as any user if: - a username is known AND - the correct account ID for this username is guessed AND - the account has no active 2FA (two factor) authentication Solution - The entrypoint.sh file is updated and now contains a script that generates a random APP_SECRET via bin2hex(random_bytes(32)) which will be stored in /opt/kimai/var/data/.appsecret - The entrypoint.sh will create the file /opt/kimai/.env.local containing the APP_SECRET, either fetched from the Docker Environment or from the newly created secret file - The documentation was u