SSH supports two different and incompatible protocols: SSH1 and SSH2. SSH1 was the original protocol and was subject to security issues. SSH2 is more advanced and secure.
Rationale
SSH v1 suffers from insecurities that do not affect SSH v2.
Audit Procedure
Using Command Line
To verify the correct SSH setting, run the following command and verify that the output is as shown:
grep "^Protocol" /etc/ssh/sshd_config
Expected Result
Protocol 2
Remediation
Using Command Line
Edit the /etc/ssh/sshd_config file to set the parameter as follows:
Protocol 2
Default Value
Protocol 2
References
CIS Ubuntu 12.04 LTS Server Benchmark v1.1.0
Profile
Level 1 - Scored
1---2name: cis-ubuntu1204-v110-9-3-13description: Set SSH Protocol to 24---56# 9.3.1 Set SSH Protocol to 2 (Scored)78## Profile Applicability910- Level 11112## Description1314SSH supports two different and incompatible protocols: SSH1 and SSH2. SSH1 was the original protocol and was subject to security issues. SSH2 is more advanced and secure.1516## Rationale1718SSH v1 suffers from insecurities that do not affect SSH v2.1920## Audit Procedure2122### Using Command Line2324To verify the correct SSH setting, run the following command and verify that the output is as shown:2526```bash27grep "^Protocol" /etc/ssh/sshd_config28```2930## Expected Result3132```33Protocol 234```3536## Remediation3738### Using Command Line3940Edit the `/etc/ssh/sshd_config` file to set the parameter as follows:4142```bash43Protocol 244```4546## Default Value4748Protocol 24950## References5152- CIS Ubuntu 12.04 LTS Server Benchmark v1.1.05354## Profile5556Level 1 - Scored
Run npx skillmds@latest add cyberstrikeus/cis-ubuntu1204-v110-9-3-1 in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.
Set SSH Protocol to 2 It is listed under Coding & Dev Tools on SkillMD.
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cyberstrikeus (@cyberstrikeus) published this skill. Their other Agent Skills are listed on their SkillMD profile.
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