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Skillsmacos-security-baseline

macos-security-baseline

Security & auditing

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Updated 10-16 09:49

About this skill

macOS Security Baseline

Enables the three security wins every developer Mac should have — FileVault, firewall, Touch ID for sudo — without ever weakening macOS protections. A dev machine holds SSH keys, cloud sessions, and source code: treat it as a privileged endpoint.

When NOT to use

  • OS updates, Command Line Tools, Rosetta → macos-system-prep
  • SSH keys, commit signing, GitHub auth → git-ssh-identity
  • "App is blocked by Gatekeeper" → not this skill's job; never disable Gatekeeper globally (spctl --master-disable was removed in Sequoia). Point the user at the per-app System Settings override and stop.
  • Finder/Dock/keyboard tweaks → macos-defaults

Safety rails

  • FileVault recovery key: instruct the user to store it in a password manager. Never ask for it, never echo it, never write it to a file. It must not appear in this chat.
  • PAM changes gate sudo itself — always back up first, keep a working root terminal open while testing, and verify in a new shell before closing.
  • Ask consent before every sudo command here.
  • Never automate security weakening (Gatekeeper exceptions, firewall off, SIP changes) — refuse and explain.

Workflow

1. FileVault (manual, user-driven)

Check state (read-only): fdesetup status

If off, have the user enable it themselves: System Settings → Privacy & Security → FileVault → Turn On. They choose iCloud escrow (no key to store — recovery goes through the Apple Account) or a personal recovery key, which must go immediately into their password manager (somewhere accessible off this device) — never into this session. Encryption may show "in progress" for a while; that counts as done here. Do not run sudo fdesetup enable — the GUI flow handles the recovery ceremony correctly.

2. Application firewall

Check both state and policy (read-only):

/usr/libexec/ApplicationFirewall/socketfilterfw --getglobalstate
/usr/libexec/ApplicationFirewall/socketfilterfw --getblockall

Enable via System Settings → Network → Firewall, or with consent:

sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setglobalstate on

If "block all incoming" is already ON, that's an existing deliberate policy — report it and leave it (turning it off would be an automated weakening); just note it blocks reaching local dev servers from other devices. For fresh setups, the default per-app prompting is right.

3. Touch ID for sudo

The update-surviving mechanism (macOS Sonoma+) is /etc/pam.d/sudo_local — never edit /etc/pam.d/sudo, which macOS updates overwrite. With consent:

Three cases — never blindly overwrite an existing sudo_local (it may carry customization like pam_reattach):

# Case 1: pam_tid already active - done, touch nothing
sudo grep -q '^auth.*pam_tid' /etc/pam.d/sudo_local 2>/dev/null && echo "already enabled"

# Case 2: file exists WITHOUT active pam_tid - show it, timestamped backup,
# then uncomment/insert ONLY the pam_tid line (anchored pattern; keep the rest)
sudo cp /etc/pam.d/sudo_local "/etc/pam.d/sudo_local.bak.$(date +%Y%m%d%H%M%S)"
sudo sed -i '' 's/^#auth\([[:space:]]*sufficient[[:space:]]*pam_tid.so\)/auth\1/' /etc/pam.d/sudo_local
sudo grep -q '^auth.*pam_tid' /etc/pam.d/sudo_local || \
  printf 'auth       sufficient     pam_tid.so\n' | sudo tee -a /etc/pam.d/sudo_local >/dev/null

# Case 3: no file - create from Apple's template (anchored uncomment;
# full-string seds silently no-op on the template's whitespace)
sed -e 's/^#auth/auth/' /etc/pam.d/sudo_local.template | sudo tee /etc/pam.d/sudo_local >/dev/null

(tee under sudo writes the file root-owned with default 0644 — correct for PAM; confirm with stat -f '%Su %OLp' /etc/pam.d/sudo_local.)

Verify in a new terminal (keep the current one open as a fallback):

sudo -k && sudo true   # should prompt for Touch ID, not password

Caveats worth stating when relevant:

  • Works out of the box in Terminal, Ghostty, kitty, Alacritty, VS Code's terminal. iTerm2 needs Settings → Advanced → "Allow sessions to survive logging out and back in" set to No.
  • Inside tmux, Touch ID needs the third-party pam_reattach module (brew install pam-reattach, add its line to sudo_local) — optional.
  • After a macOS update, if Touch ID sudo stops working, check that /etc/pam.d/sudo_local still exists (it should — that's the point) and that nobody had edited /etc/pam.d/sudo instead.

4. Leave the rest alone

Gatekeeper, SIP, automatic security responses, and background system-data updates stay on. If a tool demands disabling any of them, that is a red flag to investigate, not a setup step.

5. Verify

sh "${CLAUDE_SKILL_DIR}/scripts/check.sh"

Output spec

Done means: fdesetup status reports FileVault On or "encryption in progress" (or the user explicitly deferred), firewall global state is enabled, and Touch ID sudo is in one of three recorded states — enabled (verified in a fresh shell), unavailable (no Touch ID hardware — password fallback is fine, not a failure), or deferred by the user. No security feature was weakened. Report actual command output.

Gotchas

  • sed 's/#auth sufficient pam_tid.so/.../' style full-string matches fail when Apple changes template spacing — always anchor on ^#auth.
  • Touch ID sudo doesn't work over SSH sessions or in su shells — password fallback still applies (pam_tid is sufficient, not required, so nothing breaks).
  • On Macs without Touch ID (external non-Touch keyboards, clamshell mode), the password prompt appears as usual; Apple Watch approval works if enabled in System Settings.