f374ba41f5
Release notes are available at https://www.openssh.com/txt/release-9.2 OpenSSH 9.2 contains fixes for two security problems and a memory safety problem. The memory safety problem is not believed to be exploitable. These fixes have already been committed to OpenSSH 9.1 in FreeBSD. Some other notable items from the release notes: * ssh(1): add a new EnableEscapeCommandline ssh_config(5) option that controls whether the client-side ~C escape sequence that provides a command-line is available. Among other things, the ~C command-line could be used to add additional port-forwards at runtime. * sshd(8): add support for channel inactivity timeouts via a new sshd_config(5) ChannelTimeout directive. This allows channels that have not seen traffic in a configurable interval to be automatically closed. Different timeouts may be applied to session, X11, agent and TCP forwarding channels. * sshd(8): add a sshd_config UnusedConnectionTimeout option to terminate client connections that have no open channels for a length of time. This complements the ChannelTimeout option above. * sshd(8): add a -V (version) option to sshd like the ssh client has. * scp(1), sftp(1): add a -X option to both scp(1) and sftp(1) to allow control over some SFTP protocol parameters: the copy buffer length and the number of in-flight requests, both of which are used during upload/download. Previously these could be controlled in sftp(1) only. This makes them available in both SFTP protocol clients using the same option character sequence. * ssh-keyscan(1): allow scanning of complete CIDR address ranges, e.g. "ssh-keyscan 192.168.0.0/24". If a CIDR range is passed, then it will be expanded to all possible addresses in the range including the all-0s and all-1s addresses. bz#976 * ssh(1): support dynamic remote port forwarding in escape command-line's -R processing. bz#3499 MFC after: 1 week Sponsored by: The FreeBSD Foundation
179 lines
4.4 KiB
Groff
179 lines
4.4 KiB
Groff
.\" $OpenBSD: ssh-keyscan.1,v 1.47 2022/10/28 02:29:34 djm Exp $
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.\"
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.\" Copyright 1995, 1996 by David Mazieres <dm@lcs.mit.edu>.
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.\"
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.\" Modification and redistribution in source and binary forms is
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.\" permitted provided that due credit is given to the author and the
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.\" OpenBSD project by leaving this copyright notice intact.
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.\"
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.Dd $Mdocdate: October 28 2022 $
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.Dt SSH-KEYSCAN 1
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.Os
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.Sh NAME
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.Nm ssh-keyscan
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.Nd gather SSH public keys from servers
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.Sh SYNOPSIS
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.Nm ssh-keyscan
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.Op Fl 46cDHv
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.Op Fl f Ar file
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.Op Fl p Ar port
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.Op Fl T Ar timeout
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.Op Fl t Ar type
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.Op Ar host | addrlist namelist
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.Sh DESCRIPTION
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.Nm
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is a utility for gathering the public SSH host keys of a number of
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hosts.
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It was designed to aid in building and verifying
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.Pa ssh_known_hosts
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files,
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the format of which is documented in
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.Xr sshd 8 .
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.Nm
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provides a minimal interface suitable for use by shell and perl
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scripts.
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.Pp
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.Nm
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uses non-blocking socket I/O to contact as many hosts as possible in
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parallel, so it is very efficient.
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The keys from a domain of 1,000
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hosts can be collected in tens of seconds, even when some of those
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hosts are down or do not run
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.Xr sshd 8 .
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For scanning, one does not need
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login access to the machines that are being scanned, nor does the
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scanning process involve any encryption.
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.Pp
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Hosts to be scanned may be specified by hostname, address or by CIDR
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network range (e.g. 192.168.16/28).
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If a network range is specified, then all addresses in that range will
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be scanned.
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.Pp
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The options are as follows:
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.Bl -tag -width Ds
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.It Fl 4
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Force
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.Nm
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to use IPv4 addresses only.
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.It Fl 6
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Force
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.Nm
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to use IPv6 addresses only.
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.It Fl c
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Request certificates from target hosts instead of plain keys.
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.It Fl D
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Print keys found as SSHFP DNS records.
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The default is to print keys in a format usable as a
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.Xr ssh 1
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.Pa known_hosts
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file.
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.It Fl f Ar file
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Read hosts or
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.Dq addrlist namelist
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pairs from
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.Ar file ,
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one per line.
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If
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.Sq -
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is supplied instead of a filename,
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.Nm
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will read from the standard input.
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Names read from a file must start with an address, hostname or CIDR network
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range to be scanned.
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Addresses and hostnames may optionally be followed by comma-separated name
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or address aliases that will be copied to the output.
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For example:
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.Bd -literal
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192.168.11.0/24
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10.20.1.1
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happy.example.org
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10.0.0.1,sad.example.org
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.Ed
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.It Fl H
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Hash all hostnames and addresses in the output.
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Hashed names may be used normally by
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.Xr ssh 1
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and
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.Xr sshd 8 ,
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but they do not reveal identifying information should the file's contents
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be disclosed.
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.It Fl p Ar port
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Connect to
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.Ar port
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on the remote host.
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.It Fl T Ar timeout
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Set the timeout for connection attempts.
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If
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.Ar timeout
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seconds have elapsed since a connection was initiated to a host or since the
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last time anything was read from that host, the connection is
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closed and the host in question considered unavailable.
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The default is 5 seconds.
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.It Fl t Ar type
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Specify the type of the key to fetch from the scanned hosts.
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The possible values are
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.Dq dsa ,
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.Dq ecdsa ,
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.Dq ed25519 ,
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.Dq ecdsa-sk ,
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.Dq ed25519-sk ,
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or
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.Dq rsa .
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Multiple values may be specified by separating them with commas.
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The default is to fetch
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.Dq rsa ,
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.Dq ecdsa ,
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.Dq ed25519 ,
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.Dq ecdsa-sk ,
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and
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.Dq ed25519-sk
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keys.
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.It Fl v
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Verbose mode:
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print debugging messages about progress.
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.El
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.Pp
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If an ssh_known_hosts file is constructed using
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.Nm
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without verifying the keys, users will be vulnerable to
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.Em man in the middle
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attacks.
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On the other hand, if the security model allows such a risk,
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.Nm
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can help in the detection of tampered keyfiles or man in the middle
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attacks which have begun after the ssh_known_hosts file was created.
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.Sh FILES
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.Pa /etc/ssh/ssh_known_hosts
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.Sh EXAMPLES
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Print the RSA host key for machine
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.Ar hostname :
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.Pp
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.Dl $ ssh-keyscan -t rsa hostname
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.Pp
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Search a network range, printing all supported key types:
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.Pp
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.Dl $ ssh-keyscan 192.168.0.64/25
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.Pp
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Find all hosts from the file
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.Pa ssh_hosts
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which have new or different keys from those in the sorted file
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.Pa ssh_known_hosts :
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.Bd -literal -offset indent
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$ ssh-keyscan -t rsa,dsa,ecdsa,ed25519 -f ssh_hosts | \e
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sort -u - ssh_known_hosts | diff ssh_known_hosts -
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.Ed
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.Sh SEE ALSO
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.Xr ssh 1 ,
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.Xr sshd 8
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.Rs
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.%D 2006
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.%R RFC 4255
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.%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints
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.Re
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.Sh AUTHORS
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.An -nosplit
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.An David Mazieres Aq Mt dm@lcs.mit.edu
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wrote the initial version, and
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.An Wayne Davison Aq Mt wayned@users.sourceforge.net
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added support for protocol version 2.
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