[MEDIUM] [Security] Insecure Default Database Credentials

[bigtcze]

Severity: Medium
Description: The database connection logic uses hardcoded default credentials (noteer / noteer) when environment variables are missing. This poses a risk if the application is deployed without explicit configuration.
Complexity: 2
Permalink: https://github.com/bigtcze/noteer/blob/main/backend/src/db/index.js#L52-L56