Universal sysadmin credential vulnerability in Jumis

Jumis (formerly Tildes Jumis) creates and uses a Microsoft SQL Server login named ##Tilde_JumisAdmin## whose password is derived deterministically from a single non-secret input - the SQL Server name (@@servername). The derivation algorithm is hard-coded in the client application and is identical across every installation; it contains a hard-coded secret key for entropy. Because the only input (the server name) is not secret - the instance suffix is hard-coded and the host name is discoverable via the SQL Server Browser service (UDP 1434), the TDS pre-login response, or DNS/NetBIOS - any party able to reach a Jumis SQL Server can compute the password offline and authenticate. The ##Tilde_JumisAdmin## login is a member of the sysadmin server role. Successful authentication therefore grants full administrative control of the SQL Server instance and read/write access to every customer's accounting database hosted on it. The on-premise server installation also programmatically enables xp_cmdshell during routine operation, so sysadmin access escalates to operating-system command execution on the database server.