Hi all,

Thanks to Jerome, there is now SSH2DOS in the FreeDOS net repo, which is great!

Unfortunately even this free SSH client is getting a bit rusty, the latest 
version is 11 years old.

As I found out, it wouldn’t connect to my server (Ubuntu 16.04 LTS). 
But it still connected fine to a Debian Wheezy machine.

In the end I found the problem: OpenSSH versions >=6.7 have disabled a 
necessary KexAlgorithm and a Cipher.

Here is a report. I also posted it on the SSH2DOS page on SourceForge.

Hope this helps others eventually...
Ulrich



1. The solution:

Add the following lines to /etc/ssh/sshd_config on the server:

Ciphers aes128-cbc
KexAlgorithms diffie-hellman-group-exchange-sha1


2. The problem:

SSH2DOS works fine with a Debian Wheezy machine with OpenSSH 6.0.

But it does not connect to a Debian 8 machine with OpenSSH 6.7.
It also does not connect to a Ubuntu 16.04 server with OpenSSH 7.2.

SSH2DOS gives the following error code:

C:\> ssh2d386 username 192.168.1.136
SSH2DOS v0.2.1. 386+ version
Remote host closed connection
DH key exchange failed
Socket write error. File: transprt.c, line:698
Remote reset connection

On the server /var/log/auth.log says:
Jan 23 00:17:25 debian8 sshd [1883]: fatal: Unable to negotiate a key exchange 
method [preauth]

SSH2D386 with the -d option writes the following DEBUG.PKT:


-------------------

RECEIVED packet:
14 63 99 7B 69 DA 8E 90 00 02 0A 69 D1 32 93 26 
E1 00 00 00 96 63 75 72 76 65 32 35 35 31 39 2D 
73 68 61 32 35 36 40 6C 69 62 73 73 68 2E 6F 72 
67 2C 65 63 64 68 2D 73 68 61 32 2D 6E 69 73 74 
70 32 35 36 2C 65 63 64 68 2D 73 68 61 32 2D 6E 
69 73 74 70 33 38 34 2C 65 63 64 68 2D 73 68 61 
32 2D 6E 69 73 74 70 35 32 31 2C 64 69 66 66 69 
65 2D 68 65 6C 6C 6D 61 6E 2D 67 72 6F 75 70 2D 
65 78 63 68 61 6E 67 65 2D 73 68 61 32 35 36 2C 
64 69 66 66 69 65 2D 68 65 6C 6C 6D 61 6E 2D 67 
72 6F 75 70 31 34 2D 73 68 61 31 00 00 00 41 73 
73 68 2D 72 73 61 2C 72 73 61 2D 73 68 61 32 2D 
35 31 32 2C 72 73 61 2D 73 68 61 32 2D 32 35 36 
2C 65 63 64 73 61 2D 73 68 61 32 2D 6E 69 73 74 
70 32 35 36 2C 73 73 68 2D 65 64 32 35 35 31 39 
00 00 00 6C 63 68 61 63 68 61 32 30 2D 70 6F 6C 
79 31 33 30 35 40 6F 70 65 6E 73 73 68 2E 63 6F 
6D 2C 61 65 73 31 32 38 2D 63 74 72 2C 61 65 73 
31 39 32 2D 63 74 72 2C 61 65 73 32 35 36 2D 63 
74 72 2C 61 65 73 31 32 38 2D 67 63 6D 40 6F 70 
65 6E 73 73 68 2E 63 6F 6D 2C 61 65 73 32 35 36 
2D 67 63 6D 40 6F 70 65 6E 73 73 68 2E 63 6F 6D 
00 00 00 6C 63 68 61 63 68 61 32 30 2D 70 6F 6C 
79 31 33 30 35 40 6F 70 65 6E 73 73 68 2E 63 6F 
6D 2C 61 65 73 31 32 38 2D 63 74 72 2C 61 65 73 
31 39 32 2D 63 74 72 2C 61 65 73 32 35 36 2D 63 
74 72 2C 61 65 73 31 32 38 2D 67 63 6D 40 6F 70 
65 6E 73 73 68 2E 63 6F 6D 2C 61 65 73 32 35 36 
2D 67 63 6D 40 6F 70 65 6E 73 73 68 2E 63 6F 6D 
00 00 00 D5 75 6D 61 63 2D 36 34 2D 65 74 6D 40 
6F 70 65 6E 73 73 68 2E 63 6F 6D 2C 75 6D 61 63 
2D 31 32 38 2D 65 74 6D 40 6F 70 65 6E 73 73 68 
2E 63 6F 6D 2C 68 6D 61 63 2D 73 68 61 32 2D 32 
35 36 2D 65 74 6D 40 6F 70 65 6E 73 73 68 2E 63 
6F 6D 2C 68 6D 61 63 2D 73 68 61 32 2D 35 31 32 
2D 65 74 6D 40 6F 70 65 6E 73 73 68 2E 63 6F 6D 
2C 68 6D 61 63 2D 73 68 61 31 2D 65 74 6D 40 6F 
70 65 6E 73 73 68 2E 63 6F 6D 2C 75 6D 61 63 2D 
36 34 40 6F 70 65 6E 73 73 68 2E 63 6F 6D 2C 75 
6D 61 63 2D 31 32 38 40 6F 70 65 6E 73 73 68 2E 
63 6F 6D 2C 68 6D 61 63 2D 73 68 61 32 2D 32 35 
36 2C 68 6D 61 63 2D 73 68 61 32 2D 35 31 32 2C 
68 6D 61 63 2D 73 68 61 31 00 00 00 D5 75 6D 61 
63 2D 36 34 2D 65 74 6D 40 6F 70 65 6E 73 73 68 
2E 63 6F 6D 2C 75 6D 61 63 2D 31 32 38 2D 65 74 
6D 40 6F 70 65 6E 73 73 68 2E 63 6F 6D 2C 68 6D 
61 63 2D 73 68 61 32 2D 32 35 36 2D 65 74 6D 40 
6F 70 65 6E 73 73 68 2E 63 6F 6D 2C 68 6D 61 63 
2D 73 68 61 32 2D 35 31 32 2D 65 74 6D 40 6F 70 
65 6E 73 73 68 2E 63 6F 6D 2C 68 6D 61 63 2D 73 
68 61 31 2D 65 74 6D 40 6F 70 65 6E 73 73 68 2E 
63 6F 6D 2C 75 6D 61 63 2D 36 34 40 6F 70 65 6E 
73 73 68 2E 63 6F 6D 2C 75 6D 61 63 2D 31 32 38 
40 6F 70 65 6E 73 73 68 2E 63 6F 6D 2C 68 6D 61 
63 2D 73 68 61 32 2D 32 35 36 2C 68 6D 61 63 2D 
73 68 61 32 2D 35 31 32 2C 68 6D 61 63 2D 73 68 
61 31 00 00 00 15 6E 6F 6E 65 2C 7A 6C 69 62 40 
6F 70 65 6E 73 73 68 2E 63 6F 6D 00 00 00 15 6E 
6F 6E 65 2C 7A 6C 69 62 40 6F 70 65 6E 73 73 68 
2E 63 6F 6D 00 00 00 00 00 00 00 00 00 00 00 00 
00 
.c.{i......i.2.&
.....curve25519-
sha...@libssh.or
g,ecdh-sha2-nist
p256,ecdh-sha2-n
istp384,ecdh-sha
2-nistp521,diffi
e-hellman-group-
exchange-sha256,
diffie-hellman-g
roup14-sha1...As
sh-rsa,rsa-sha2-
512,rsa-sha2-256
,ecdsa-sha2-nist
p256,ssh-ed25519
...lchacha20-pol
y1...@openssh.co
m,aes128-ctr,aes
192-ctr,aes256-c
tr,aes128-gcm@op
enssh.com,aes256
-g...@openssh.com
...lchacha20-pol
y1...@openssh.co
m,aes128-ctr,aes
192-ctr,aes256-c
tr,aes128-gcm@op
enssh.com,aes256
-g...@openssh.com
....umac-64-etm@
openssh.com,umac
-128-etm@openssh
.com,hmac-sha2-2
56-etm@openssh.c
om,hmac-sha2-512
-e...@openssh.com
,hmac-sha1-etm@o
penssh.com,umac-
6...@openssh.com,u
mac-128@openssh.
com,hmac-sha2-25
6,hmac-sha2-512,
hmac-sha1....uma
c-64-etm@openssh
.com,umac-128-et
m...@openssh.com,hm
ac-sha2-256-etm@
openssh.com,hmac
-sha2-512-etm@op
enssh.com,hmac-s
ha1-etm@openssh.
com,umac-64@open
ssh.com,umac-128
@openssh.com,hma
c-sha2-256,hmac-
sha2-512,hmac-sh
a1....none,zlib@
openssh.com....n
one,zlib@openssh
.com............
.

SENT packet:
14 8D 73 ED D0 96 BE 48 9A 89 61 74 E7 41 14 CE 
FC 00 00 00 22 64 69 66 66 69 65 2D 68 65 6C 6C 
6D 61 6E 2D 67 72 6F 75 70 2D 65 78 63 68 61 6E 
67 65 2D 73 68 61 31 00 00 00 07 73 73 68 2D 64 
73 73 00 00 00 0A 61 65 73 31 32 38 2D 63 62 63 
00 00 00 0A 61 65 73 31 32 38 2D 63 62 63 00 00 
00 09 68 6D 61 63 2D 73 68 61 31 00 00 00 09 68 
6D 61 63 2D 73 68 61 31 00 00 00 09 6E 6F 6E 65 
2C 7A 6C 69 62 00 00 00 09 6E 6F 6E 65 2C 7A 6C 
69 62 00 00 00 00 00 00 00 00 00 00 00 00 00 
..s....H..at.A..
...."diffie-hell
man-group-exchan
ge-sha1....ssh-d
ss....aes128-cbc
....aes128-cbc..
..hmac-sha1....h
mac-sha1....none
,zlib....none,zl
ib.............

SENT packet:
1E 00 00 04 00 
.....

SENT packet:
62 00 00 00 00 00 00 00 07 70 74 79 2D 72 65 71 
01 00 00 00 05 78 74 65 72 6D 00 00 00 50 00 00 
00 18 00 00 00 00 00 00 00 00 00 00 00 00 
b........pty-req
.....xterm...P..
..............
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