Previously /etc/ssh/sshd_config.d/99-banger.conf landed with:
LogLevel DEBUG3
PermitRootLogin yes
PubkeyAuthentication yes
AuthorizedKeysFile /root/.ssh/authorized_keys
StrictModes no
DEBUG3 was debug leftover that floods journald in normal use.
StrictModes no was a workaround for /root perm drift on the work
disk — the real fix is to make those perms correct at provisioning
time.
New drop-in:
PermitRootLogin prohibit-password
PubkeyAuthentication yes
PasswordAuthentication no
KbdInteractiveAuthentication no
AuthorizedKeysFile /root/.ssh/authorized_keys
prohibit-password blocks password root login even if PasswordAuth
gets flipped on elsewhere; KbdInteractiveAuth no closes the last
interactive fallback; StrictModes is now on (sshd's default).
normaliseHomeDirPerms chown/chmods /root to 0755 root:root at every
work-disk mount (ensureAuthorizedKeyOnWorkDisk,
seedAuthorizedKeyOnExt4Image); the .ssh dir also explicitly
chown'd root:root. Verified end-to-end against a real VM:
`sshd -T` reports strictmodes yes and all five directives match.
Regression test (sshd_config_test.go) pins the allow-list and the
deny-list (DEBUG3, StrictModes no, bare `PermitRootLogin yes`) so
the next accidental reintroduction fails fast.
README's Security section updated to reflect the new posture.
Thales Maciel
2e6e64bc04