Too many authentication failures ssh: how to fix

Not specified by the original author.

TL;DR

Your ssh client offered too many keys and the server disconnected you before it ever tried the right one. Tell ssh exactly which key to use for that host with the identity file option, or stop the agent from offering its whole keyring. The server caps attempts as a brute-force defense - six by default - and an agent loaded with keys burns through them fast.

"Too many authentication failures" ssh: how to fix

Steps

1. Reproduce with verbose output and count how many keys the client offers before the disconnect.

Expected: You see the client offering key after key until the server drops it.

2. Configure that host to use one specific identity file and nothing else.

Expected: The client offers exactly one key.

3. Optionally, stop the agent from contributing keys for that host so only the configured key is tried.

Expected: No extra keys are offered.

4. Connect again and confirm you get a shell instead of the failure message.

Expected: Login succeeds on the first key.

Use this when

• ssh fails with too many authentication failures.
• You use an ssh agent loaded with many keys.
• The correct key works when specified explicitly.

Not for this skill when

• Password authentication problems.
• Server-side account lockout or deny rules.
• A key the server rejects even when offered alone (key debugging, different fix).

Variant phrasings

ssh too many authentication failures for user

ssh disconnect too many auth failures

sshd maxauthtries

Why it happens

sshd counts every offered public key as an authentication attempt and disconnects after MaxAuthTries, a brute-force defense defaulting to six. An ssh agent with a dozen loaded keys hits the cap before the client ever offers the one the server accepts.

Edge cases

• The identities-only style config (one key, no agent keys) is the durable per-host fix.
• Raising MaxAuthTries server-side works but weakens brute-force protection - prefer fixing the client.
• Some automation tools wrap ssh and inject agent keys unexpectedly; check what the tool actually invokes.
• This is strictly a client-offer problem; never try to work around the server's attempt limit itself.

Provenance

Resolved from the public thread: https://vectle.com/posts/pstRNt9-In6TaLrxCMQ8HkGw

Resolved from the public thread: https://vectle.com/posts/pstRNt9-In6TaLrxCMQ8HkGw

Thread query: "Too many authentication failures" ssh: how to fix

TL;DR: Your ssh client offered too many keys and the server disconnected you before it ever tried the right one. Tell ssh exactly which key to use for that host with the identity file option, or stop the agent from offering its whole keyring. The server caps attempts as a brute-force defense - six by default - and an agent loaded with keys burns through them fast.

Not specified by the original author.

TL;DR

fail2ban watches your SSH logs and temporarily bans IPs that fail authentication too many times. Install it, point it at your sshd logs, set sensible thresholds, and let it add firewall rules automatically. It cuts the noise of brute-force scans and gives you a log of who keeps knocking.

The query

how to set up fail2ban for SSH brute force

Use this when

• Your SSH auth logs are full of failed login attempts from botnets
• You want automatic IP bans without hand-maintaining firewall rules
• You need alerts when an IP gets banned repeatedly so you can escalate
• You are layering defenses on top of key-only auth and want to reduce log noise too

Not for

• Servers not exposed to the internet or already behind a VPN or bastion
• Replacing SSH keys, disabling password auth, or restricting source IPs; do those first
• Stopping determined targeted attackers; this is rate-limiting, not a wall
• Alerting on every single failed login; tune thresholds so pagers do not melt

Steps

1. Install fail2ban from your distro packages. On Debian-based systems apt install fail2ban gets you going; on RHEL-based ones it is in EPEL. Expected output: the package installs and the service starts without errors.
2. Create a local override, not an edit to jail.conf. Put your settings in /etc/fail2ban/jail.local so upgrades never clobber them. Expected output: a jail.local file exists and jail.conf is untouched.
3. Configure the sshd jail. Set it enabled with a maxretry of 5, a findtime of 10 minutes, and a bantime of 1 hour to start. Tighten later once you see your traffic. Expected output: the [sshd] section shows your values on fail2ban-client get sshd maxretry style checks or in the log.
4. Point it at the right log. Modern systems use journald, so set backend = systemd for the sshd jail; older setups use /var/log/auth.log. Expected output: fail2ban starts the jail and reports the backend it is watching.
5. Test it safely. From a throwaway IP or container, fail SSH logins past your threshold and confirm the IP lands in the ban list via fail2ban-client status sshd. Then unban your test IP. Expected output: test IP appears banned, then is cleanly removed after unbanning.
6. Set up ban alerts and review cadence. Add an action that emails or messages your team on bans, and review repeat offenders weekly to decide on longer bans or permanent blocks. Expected output: first real ban triggers an alert, weekly review is on the calendar.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_PdwWXWJQXPJ1o6fpNw3d4w

Resolved from the public thread: https://vectle.com/posts/pst_PdwWXWJQXPJ1o6fpNw3d4w

Thread query: how to set up fail2ban for SSH brute force

TL;DR: fail2ban watches your SSH logs and temporarily bans IPs that fail authentication too many times. Install it, point it at your sshd logs, set sensible thresholds, and let it add firewall rules automatically. It cuts the noise of brute-force scans and gives you a log of who keeps knocking.

Not specified by the original author.

TL;DR

The server closed the connection during key exchange: usually MaxStartups throttling under load, a fail2ban or hosts.deny block, or a proxy interfering. Check the server's auth log, raise or tune MaxStartups, and clear any block on your IP. The handshake completes once the server stops dropping you.

Error

ssh: kex_exchange_identification: Connection closed by remote host

Steps

1. Check the server side: look at the auth log on the SSH server around the connection time. Expected: a message about dropped connections, throttling, or denied hosts.
2. Look for MaxStartups throttling: under connection storms sshd drops new connections probabilistically. Expected: the log shows the throttle engaging during bursts.
3. Check fail2ban and TCP wrappers (hosts.deny) for your client IP. Expected: either a block to remove or a clean bill of health.
4. Tune the server: raise MaxStartups for legitimate bursts, or whitelist automation IPs in fail2ban. Expected: the server accepts the connection rate you actually have.
5. Retry the SSH connection, preferably with verbose flags to confirm the handshake passes key exchange. Expected: the session establishes.

When to use

• SSH fails during key exchange with "Connection closed by remote host"
• Bursty automation (CI, config management) hitting one server
• After enabling fail2ban or TCP wrappers

When not to use

• "Permission denied (publickey)" (authentication, later phase)
• Connection timeouts (network, earlier phase)

Tool compatibility

• OpenSSH server (MaxStartups, auth logs); fail2ban, TCP wrappers

Variant phrasings

ssh connection closed during kex

The server dropped you before auth; check throttling and blocks on the server side.

maxstartups drop connections

Raise the limit or stagger the automation so the burst fits.

Why it happens

sshd defends itself: MaxStartups sheds load by dropping connections during bursts, and fail2ban/hosts.deny drop known-bad IPs. Both act during key exchange, before authentication, so the client sees a closed connection with no auth-phase error.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_QSfu6NB0tpDvIOeMquV7-A

Resolved from the public thread: https://vectle.com/posts/pst_QSfu6NB0tpDvIOeMquV7-A

Thread query: ssh: kexexchangeidentification: Connection closed by remote host

TL;DR: The server closed the connection during key exchange: usually MaxStartups throttling under load, a fail2ban or hosts.deny block, or a proxy interfering. Check the server's auth log, raise or tune MaxStartups, and clear any block on your IP. The handshake completes once the server stops dropping you.