FreeBSD 14 – SSH Public Key Authentication Fails – Permission and Algorithm Fix

📖 ~1 min read

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

Users with valid keys are rejected, disrupting administrative access workflows.

Environment & Reproduction

Frequently happens after home directory permission drift or sshd hardening updates.

sshd -T | egrep 'pubkeyauthentication|authorizedkeysfile'
ls -ld ~ ~/.ssh ~/.ssh/authorized_keys

Root Cause Analysis

OpenSSH rejects keys when file permissions or allowed algorithms violate policy.

Quick Triage

Run a verbose SSH client test and inspect server auth logs immediately.

ssh -vv user@host
tail -n 100 /var/log/auth.log

Step-by-Step Diagnosis

Check ownership, mode bits, and algorithm compatibility across client/server.

stat -f '%Su %Sp %N' ~/.ssh ~/.ssh/authorized_keys
ssh -Q key

Solution – Primary Fix

Correct ownership/modes, refresh authorized keys, and reload sshd safely.

chown -R user:user ~/.ssh
chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys
service sshd reload

Solution – Alternative Approaches

Use centralized SSH CA signing to reduce per-host authorized_keys complexity.

Verification & Acceptance Criteria

Key-based login succeeds without password fallback and logs show accepted key.

ssh -o PreferredAuthentications=publickey user@host 'id'

Rollback Plan

Restore previous sshd_config and authorized_keys backups if lockout risk appears.

Prevention & Hardening

Audit SSH file permissions routinely and enforce approved key algorithms.

Related Errors & Cross-Refs

Permission denied (publickey), Authentication refused: bad ownership or modes.

Related tutorial: View the step-by-step tutorial for freebsd-14.

View all freebsd-14 tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

OpenSSH hardening docs and FreeBSD sshd operational guidance.