diff --git a/src/NexusReader.Data/Persistence/DbInitializer.cs b/src/NexusReader.Data/Persistence/DbInitializer.cs
index 047b2f5..fc84c56 100644
--- a/src/NexusReader.Data/Persistence/DbInitializer.cs
+++ b/src/NexusReader.Data/Persistence/DbInitializer.cs
@@ -72,8 +72,28 @@ public static class DbInitializer
 
                 var adminPassword = configuration?["Nexus:AdminPassword"] 
                                     ?? configuration?["NEXUS_ADMIN_PASSWORD"] 
-                                    ?? Environment.GetEnvironmentVariable("NEXUS_ADMIN_PASSWORD") 
-                                    ?? "Admin123!";
+                                    ?? Environment.GetEnvironmentVariable("NEXUS_ADMIN_PASSWORD");
+
+                var env = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") 
+                          ?? Environment.GetEnvironmentVariable("DOTNET_ENVIRONMENT") 
+                          ?? "Development";
+                var isDevelopment = string.Equals(env, "Development", StringComparison.OrdinalIgnoreCase);
+
+                if (string.IsNullOrEmpty(adminPassword))
+                {
+                    if (!isDevelopment)
+                    {
+                        throw new InvalidOperationException(
+                            "CRITICAL SECURITY ERROR: Admin password is NOT configured! " +
+                            "In non-Development environments (e.g. Test/Production), the admin password must be explicitly set " +
+                            "via configuration ('Nexus:AdminPassword' or 'NEXUS_ADMIN_PASSWORD') or environment variables. " +
+                            "Seeding aborted to prevent insecure credentials fallback.");
+                    }
+
+                    Console.WriteLine("[Seeder] WARNING: Admin password is not set. Falling back to default weak password 'Admin123!' in Development environment.");
+                    adminPassword = "Admin123!";
+                }
+
                 adminUser.PasswordHash = passwordHasher.HashPassword(adminUser, adminPassword);
 
                 dbContext.Users.Add(adminUser);