| SSH-AUDIT(1) | General Commands Manual | SSH-AUDIT(1) |
ssh-audit - SSH server & client configuration auditor
ssh-audit [options] <target_host>
ssh-audit analyzes the configuration of SSH servers & clients, then warns the user of weak, obsolete, and/or untested cryptographic primitives. It is very useful for hardening SSH tunnels, which by default tend to be optimized for compatibility, not security.
See <https://www.ssh-audit.com/> for official hardening guides for common platforms.
Diffie-Hellman requires the client and server to agree on a generator value and a modulus value. In the "Group Exchange" implementation of Diffie-Hellman, the client specifies the size of the modulus in bits by providing the server with minimum, preferred and maximum values. The server then finds a group that best matches the client's request, returning the corresponding generator and modulus. For a full explanation of this process see RFC 4419 and its successors.
This test acts as a client by providing an SSH server with the size of a modulus and then obtains the size of the modulus returned by the server.
Three types of syntax are supported:
1. <x[,y,...]>
A comma delimited list of modulus sizes.
A test is performed against each value in the list where it acts as the
minimum, preferred and maximum modulus size.
2. <min:pref:max[,min:pref:max,...]>
A set of three colon delimited values denoting minimum, preferred and
maximum modulus size.
A test is performed against each set.
Multiple sets can specified as a comma separated list.
3. <x-y[:step]>
A range of modulus sizes with an optional step value. Step defaults to 1
if omitted.
If the left value is greater than the right value, then the sequence
operates from right to left.
A test is performed against each value in the range where it acts as the
minimum, preferred and maximum modulus size.
Duplicates are excluded from the return value.
By default, ssh-audit performs a standard audit. That is, it enumerates all host key types, key exchanges, ciphers, MACs, and other information, then color-codes them in output to the user. Cryptographic primitives with potential issues are displayed in yellow; primitives with serious flaws are displayed in red.
When the -P/--policy option is used, ssh-audit performs a policy audit. The target's host key types, key exchanges, ciphers, MACs, and other information is compared to a set of expected values defined in the specified policy file. If everything matches, only a short message stating a passing result is reported. Otherwise, the field(s) that did not match are reported.
Policy auditing is helpful for ensuring a group of related servers are properly hardened to an exact specification.
The set of official built-in policies can be viewed with -L/--list-policies. Multiple servers can be audited with -T/--targets=<servers.txt>. Custom policies can be made from an ideal target server with -M/--make-policy=<custom_policy.txt>.
Basic server auditing:
ssh-audit localhost ssh-audit 127.0.0.1 ssh-audit 127.0.0.1:222 ssh-audit ::1 ssh-audit [::1]:222
To run a standard audit against many servers (place targets into servers.txt, one on each line in the format of HOST[:PORT]):
ssh-audit -T servers.txt
To audit a client configuration (listens on port 2222 by default; connect using "ssh -p 2222 anything@localhost"):
ssh-audit -c
To audit a client configuration, with a listener on port 4567:
ssh-audit -c -p 4567
To list all official built-in policies (hint: use their full names with -P/--policy):
ssh-audit -L
To run a built-in policy audit against a server (hint: use -L to see list of built-in policies):
ssh-audit -P "Hardened Ubuntu Server 20.04 LTS (version 1)" targetserver
To run a custom policy audit against a server (hint: use -M/--make-policy to create a custom policy file):
ssh-audit -P path/to/server_policy.txt targetserver
To run a policy audit against a client:
ssh-audit -c -P ["policy name" | path/to/client_policy.txt]
To run a policy audit against many servers:
ssh-audit -T servers.txt -P ["policy name" | path/to/server_policy.txt]
To create a policy based on a target server (which can be manually edited; see official built-in policies for syntax examples):
ssh-audit -M new_policy.txt targetserver
To run a Diffie-Hellman Group Exchange modulus size test using the values 2000 bits, 3000 bits, 4000 bits and 5000 bits:
ssh-audit targetserver --gex-test=2000,3000,4000,5000
To run a Diffie-Hellman Group Exchange modulus size test where 2048 bits is the minimum, 3072 bits is the preferred and 5000 bits is the maximum:
ssh-audit targetserver --gex-test=2048:3072:5000
To run a Diffie-Hellman Group Exchange modulus size test from 0 bits to 5120 bits in increments of 1024 bits:
ssh-audit targetserver --gex-test=0-5120:1024
When a successful connection is made and all algorithms are rated as "good", ssh-audit returns 0. Other possible return values are:
1 = connection error 2 = at least one algorithm warning was found 3 = at least one algorithm failure was found <any other non-zero value> = unknown error
Hardening guides for common platforms can be found at: <https://www.ssh-audit.com/>
Please file bug reports as a Github Issue at: <https://github.com/jtesta/ssh-audit/issues>
ssh-audit was originally written by Andris Raugulis
<moo@arthepsy.eu>, and maintained from 2015 to 2017.
Maintainership was assumed and development was resumed in 2017 by Joe Testa <jtesta@positronsecurity.com>.
| March 13, 2022 |