.TH SSH-AUDIT 1 "March 13, 2022"

.SH NAME

\fBssh-audit\fP \- SSH server & client configuration auditor

.SH SYNOPSIS

.B ssh-audit

.RI [ options ] " <target_host>"

.SH DESCRIPTION

.PP

\fBssh-audit\fP 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.

.PP

See <https://www.ssh\-audit.com/> for official hardening guides for common platforms.

.SH OPTIONS

.TP

.B -h, \-\-help

.br

Print short summary of options.

.TP

.B -1, \-\-ssh1

.br

Only perform an audit using SSH protocol version 1.

.TP

.B -2, \-\-ssh2

.br

Only perform an audit using SSH protocol version 2.

.TP

.B -4, \-\-ipv4

.br

Prioritize the usage of IPv4.

.TP

.B -6, \-\-ipv6

.br

Prioritize the usage of IPv6.

.TP

.B -b, \-\-batch

.br

Enables grepable output.

.TP

.B -c, \-\-client\-audit

.br

Starts a server on port 2222 to audit client software configuration. Use -p/--port=<port> to change port and -t/--timeout=<secs> to change listen timeout.

.TP

.B -d, \-\-debug

.br

Enable debug output.

.TP

.B -g, \-\-gex-test=<x[,y,...] | min1:pref1:max1[,min2:pref2:max2,...] | x-y[:step]>

.br

Runs a Diffie-Hellman Group Exchange modulus size test against a server.

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.

.TP

.B -j, \-\-json

.br

Output results in JSON format. Specify twice (-jj) to enable indent printing (useful for debugging).

.TP

.B -l, \-\-level=<info|warn|fail>

.br

Specify the minimum output level. Default is info.

.TP

.B -L, \-\-list-policies

.br

List all official, built-in policies for common systems. Their full names can then be passed to -P/--policy.

.TP

.B \-\-lookup=<alg1,alg2,...>

.br

Look up the security information of an algorithm(s) in the internal database. Does not connect to a server.

.TP

.B -m, \-\-manual

.br

Print the man page (Windows only).

.TP

.B -M, \-\-make-policy=<custom_policy.txt>

.br

Creates a policy based on the target server. Useful when other servers should be compared to the target server's custom configuration (i.e.: a cluster environment). Note that the resulting policy can be edited manually.

.TP

.B -n, \-\-no-colors

.br

Disable color output.

.TP

.B -p, \-\-port=<port>

.br

The TCP port to connect to when auditing a server, or the port to listen on when auditing a client.

.TP

.B -P, \-\-policy=<"built-in policy name" | path/to/custom_policy.txt>

.br

Runs a policy audit against a target using the specified policy (see \fBPOLICY AUDIT\fP section for detailed description of this mode of operation). Combine with -c/--client-audit to audit a client configuration instead of a server. Use -L/--list-policies to list all official, built-in policies for common systems.

.TP

.B -t, \-\-timeout=<secs>

.br

The timeout, in seconds, for creating connections and reading data from the socket. Default is 5.

.TP

.B -T, \-\-targets=<hosts.txt>

.br

A file containing a list of target hosts. Each line must have one host, in the format of HOST[:PORT]. Use --threads to control concurrent scans.

.TP

.B \-\-threads=<threads>

.br

The number of threads to use when scanning multiple targets (with -T/--targets). Default is 32.

.TP

.B -v, \-\-verbose

.br

Enable verbose output.

.SH STANDARD AUDIT

.PP

By default, \fBssh-audit\fP 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.

.SH POLICY AUDIT

.PP

When the -P/--policy option is used, \fBssh-audit\fP 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.

.PP

Policy auditing is helpful for ensuring a group of related servers are properly hardened to an exact specification.

.PP

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>.

.SH EXAMPLES

.LP

Basic server auditing:

.RS

.nf

ssh-audit localhost

ssh-audit 127.0.0.1

ssh-audit 127.0.0.1:222

ssh-audit ::1

ssh-audit [::1]:222

.fi

.RE

.LP

To run a standard audit against many servers (place targets into servers.txt, one on each line in the format of HOST[:PORT]):

.RS

.nf

ssh-audit -T servers.txt

.fi

.RE

.LP

To audit a client configuration (listens on port 2222 by default; connect using "ssh -p 2222 anything@localhost"):

.RS

.nf

ssh-audit -c

.fi

.RE

.LP

To audit a client configuration, with a listener on port 4567:

.RS

.nf

ssh-audit -c -p 4567

.fi

.RE

.LP

To list all official built-in policies (hint: use their full names with -P/--policy):

.RS

.nf

ssh-audit -L

.fi

.RE

.LP

To run a built-in policy audit against a server (hint: use -L to see list of built-in policies):

.RS

.nf

ssh-audit -P "Hardened Ubuntu Server 20.04 LTS (version 1)" targetserver

.fi

.RE

.LP

To run a custom policy audit against a server (hint: use -M/--make-policy to create a custom policy file):

.RS

.nf

ssh-audit -P path/to/server_policy.txt targetserver

.fi

.RE

.LP

To run a policy audit against a client:

.RS

.nf

ssh-audit -c -P ["policy name" | path/to/client_policy.txt]

.fi

.RE

.LP

To run a policy audit against many servers:

.RS

.nf

ssh-audit -T servers.txt -P ["policy name" | path/to/server_policy.txt]

.fi

.RE

.LP

To create a policy based on a target server (which can be manually edited; see official built-in policies for syntax examples):

.RS

.nf

ssh-audit -M new_policy.txt targetserver

.fi

.RE

.LP

To run a Diffie-Hellman Group Exchange modulus size test using the values 2000 bits, 3000 bits, 4000 bits and 5000 bits:

.RS

.nf

ssh-audit targetserver --gex-test=2000,3000,4000,5000

.fi

.RE

.LP

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:

.RS

.nf

ssh-audit targetserver --gex-test=2048:3072:5000

.fi

.RE

.LP

To run a Diffie-Hellman Group Exchange modulus size test from 0 bits to 5120 bits in increments of 1024 bits:

.RS

.nf

ssh-audit targetserver --gex-test=0-5120:1024

.fi

.RE

.SH RETURN VALUES

When a successful connection is made and all algorithms are rated as "good", \fBssh-audit\fP returns 0. Other possible return values are:

.RS

.nf

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

.fi

.RE

.SH SSH HARDENING GUIDES

Hardening guides for common platforms can be found at: <https://www.ssh\-audit.com/>

.SH BUG REPORTS

Please file bug reports as a Github Issue at: <https://github.com/jtesta/ssh\-audit/issues>

.SH AUTHOR

.LP

\fBssh-audit\fP was originally written by Andris Raugulis <moo@arthepsy.eu>, and maintained from 2015 to 2017.

.br

.LP

Maintainership was assumed and development was resumed in 2017 by Joe Testa <jtesta@positronsecurity.com>.