mirror of https://github.com/jtesta/ssh-audit.git
300 lines
8.6 KiB
Groff
300 lines
8.6 KiB
Groff
.TH SSH-AUDIT 1 "February 16, 2024"
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.SH NAME
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\fBssh-audit\fP \- SSH server & client configuration auditor
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.SH SYNOPSIS
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.B ssh-audit
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.RI [ options ] " <target_host>"
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.SH DESCRIPTION
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.PP
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\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.
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.PP
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See <https://www.ssh\-audit.com/> for official hardening guides for common platforms.
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.SH OPTIONS
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.TP
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.B -h, \-\-help
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.br
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Print short summary of options.
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.TP
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.B -1, \-\-ssh1
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.br
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Only perform an audit using SSH protocol version 1.
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.TP
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.B -2, \-\-ssh2
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.br
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Only perform an audit using SSH protocol version 2.
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.TP
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.B -4, \-\-ipv4
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.br
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Prioritize the usage of IPv4.
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.TP
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.B -6, \-\-ipv6
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.br
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Prioritize the usage of IPv6.
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.TP
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.B -b, \-\-batch
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.br
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Enables grepable output.
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.TP
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.B -c, \-\-client\-audit
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.br
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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.
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.TP
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.B -d, \-\-debug
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.br
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Enable debug output.
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.TP
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.B -g, \-\-gex-test=<x[,y,...] | min1:pref1:max1[,min2:pref2:max2,...] | x-y[:step]>
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.br
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Runs a Diffie-Hellman Group Exchange modulus size test against a server.
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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.
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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.
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Three types of syntax are supported:
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1. <x[,y,...]>
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A comma delimited list of modulus sizes.
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A test is performed against each value in the list where it acts as the minimum, preferred and maximum modulus size.
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2. <min:pref:max[,min:pref:max,...]>
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A set of three colon delimited values denoting minimum, preferred and maximum modulus size.
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A test is performed against each set.
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Multiple sets can specified as a comma separated list.
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3. <x-y[:step]>
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A range of modulus sizes with an optional step value. Step defaults to 1 if omitted.
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If the left value is greater than the right value, then the sequence operates from right to left.
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A test is performed against each value in the range where it acts as the minimum, preferred and maximum modulus size.
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Duplicates are excluded from the return value.
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.TP
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.B -j, \-\-json
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.br
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Output results in JSON format. Specify twice (-jj) to enable indent printing (useful for debugging).
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.TP
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.B -l, \-\-level=<info|warn|fail>
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.br
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Specify the minimum output level. Default is info.
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.TP
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.B -L, \-\-list-policies
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.br
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List all official, built-in policies for common systems. Their full names can then be passed to -P/--policy.
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.TP
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.B \-\-lookup=<alg1,alg2,...>
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.br
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Look up the security information of an algorithm(s) in the internal database. Does not connect to a server.
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.TP
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.B -m, \-\-manual
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.br
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Print the man page (Docker, PyPI, Snap, and Windows builds only).
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.TP
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.B -M, \-\-make-policy=<custom_policy.txt>
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.br
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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.
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.TP
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.B -n, \-\-no-colors
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.br
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Disable color output. Automatically set when the NO_COLOR environment variable is set.
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.TP
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.B -p, \-\-port=<port>
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.br
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The TCP port to connect to when auditing a server, or the port to listen on when auditing a client.
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.TP
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.B -P, \-\-policy=<"built-in policy name" | path/to/custom_policy.txt>
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.br
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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.
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.TP
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.B -t, \-\-timeout=<secs>
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.br
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The timeout, in seconds, for creating connections and reading data from the socket. Default is 5.
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.TP
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.B -T, \-\-targets=<hosts.txt>
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.br
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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.
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.TP
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.B \-\-threads=<threads>
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.br
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The number of threads to use when scanning multiple targets (with -T/--targets). Default is 32.
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.TP
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.B -v, \-\-verbose
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.br
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Enable verbose output.
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.SH STANDARD AUDIT
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.PP
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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.
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.SH POLICY AUDIT
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.PP
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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.
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.PP
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Policy auditing is helpful for ensuring a group of related servers are properly hardened to an exact specification.
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.PP
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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>.
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.SH EXAMPLES
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.LP
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Basic server auditing:
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.RS
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.nf
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ssh-audit localhost
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ssh-audit 127.0.0.1
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ssh-audit 127.0.0.1:222
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ssh-audit ::1
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ssh-audit [::1]:222
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.fi
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.RE
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.LP
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To run a standard audit against many servers (place targets into servers.txt, one on each line in the format of HOST[:PORT]):
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.RS
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.nf
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ssh-audit -T servers.txt
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.fi
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.RE
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.LP
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To audit a client configuration (listens on port 2222 by default; connect using "ssh -p 2222 anything@localhost"):
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.RS
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.nf
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ssh-audit -c
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.fi
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.RE
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.LP
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To audit a client configuration, with a listener on port 4567:
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.RS
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.nf
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ssh-audit -c -p 4567
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.fi
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.RE
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.LP
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To list all official built-in policies (hint: use their full names with -P/--policy):
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.RS
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.nf
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ssh-audit -L
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.fi
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.RE
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.LP
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To run a built-in policy audit against a server (hint: use -L to see list of built-in policies):
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.RS
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.nf
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ssh-audit -P "Hardened Ubuntu Server 20.04 LTS (version 1)" targetserver
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.fi
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.RE
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.LP
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To run a custom policy audit against a server (hint: use -M/--make-policy to create a custom policy file):
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.RS
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.nf
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ssh-audit -P path/to/server_policy.txt targetserver
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.fi
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.RE
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.LP
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To run a policy audit against a client:
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.RS
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.nf
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ssh-audit -c -P ["policy name" | path/to/client_policy.txt]
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.fi
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.RE
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.LP
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To run a policy audit against many servers:
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.RS
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.nf
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ssh-audit -T servers.txt -P ["policy name" | path/to/server_policy.txt]
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.fi
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.RE
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.LP
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To create a policy based on a target server (which can be manually edited; see official built-in policies for syntax examples):
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.RS
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.nf
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ssh-audit -M new_policy.txt targetserver
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.fi
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.RE
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.LP
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To run a Diffie-Hellman Group Exchange modulus size test using the values 2000 bits, 3000 bits, 4000 bits and 5000 bits:
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.RS
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.nf
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ssh-audit targetserver --gex-test=2000,3000,4000,5000
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.fi
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.RE
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.LP
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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:
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.RS
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.nf
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ssh-audit targetserver --gex-test=2048:3072:5000
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.fi
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.RE
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.LP
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To run a Diffie-Hellman Group Exchange modulus size test from 0 bits to 5120 bits in increments of 1024 bits:
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.RS
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.nf
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ssh-audit targetserver --gex-test=0-5120:1024
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.fi
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.RE
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.SH RETURN VALUES
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When a successful connection is made and all algorithms are rated as "good", \fBssh-audit\fP returns 0. Other possible return values are:
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.RS
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.nf
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1 = connection error
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2 = at least one algorithm warning was found
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3 = at least one algorithm failure was found
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<any other non-zero value> = unknown error
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.fi
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.RE
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.SH SSH HARDENING GUIDES
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Hardening guides for common platforms can be found at: <https://www.ssh\-audit.com/>
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.SH BUG REPORTS
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Please file bug reports as a Github Issue at: <https://github.com/jtesta/ssh\-audit/issues>
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.SH AUTHOR
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.LP
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\fBssh-audit\fP was originally written by Andris Raugulis <moo@arthepsy.eu>, and maintained from 2015 to 2017.
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.br
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.LP
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Maintainership was assumed and development was resumed in 2017 by Joe Testa <jtesta@positronsecurity.com>.
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