Navigate to https://mikrotik.com/download (Look for the "Archive" section or use the version selector). MikroTik often moves older versions to an archive path. The direct archive URL is typically: https://download.mikrotik.com/routeros/6.48.6/
To ensure a secure installation, always use the Official MikroTik Download Page . Mikrotik 6.48.6 Download
Version 6.48.6 predates patches for several known CVEs (Common Vulnerabilities and Exposures), including vulnerabilities in the WinBox protocol and DNS resolver. Do not expose a router running this version directly to the public internet. Navigate to https://mikrotik