Is Proxmox Backup Server 3.4.2 affected?

No known vulnerabilities affect 3.4.2 in the sources we track.

Your branch 3 has reached end of life (Aug 31, 2026).

7 newer releases in its track, up to 3.4.9. What changed up to 3.4.9

A newer release line is out: 4.2.9.