Bug 7178 - SSHD reports dispatch_protocol_error in /var/log/secure upon connection with ThinLinc client
Summary: SSHD reports dispatch_protocol_error in /var/log/secure upon connection with ...
Status: CLOSED FIXED
Alias: None
Product: ThinLinc
Classification: Unclassified
Component: Server OS (show other bugs)
Version: trunk
Hardware: PC Unknown
: P2 Normal
Target Milestone: 4.10.0
Assignee: Henrik Andersson
URL:
Keywords: prosaic, samuel_tester
Depends on:
Blocks:
 
Reported: 2018-05-17 05:32 CEST by Henrik Andersson
Modified: 2019-02-14 09:57 CET (History)
2 users (show)

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Description Henrik Andersson cendio 2018-05-17 05:32:54 CEST 
Using the native client on Linux connecting to a ThinLinc server running on RHEL6.9, the following  error message appears in /var/log/secure:

  May 17 05:22:41 castro sshd[14780]: dispatch_protocol_error: type 50 seq 4

Server running openssh-server-5.3p1-123.el6_9.x86_64

However, authentication works as expected and one could successfully continue.
Comment 2 Henrik Andersson cendio 2018-05-17 05:40:48 CEST 
Connecting using ThinLinc client against a Fedora 28 which uses openssh-server-7.7p1-3.fc28.x86_64, I get following dispatch error:

  dispatch_protocol_error: type 50 seq 3 [preauth]

Connecting using system provided ssh binary does not generate such message.
Comment 3 Henrik Andersson cendio 2018-05-17 05:51:03 CEST 
Running the ThinLinc client ssh binary by hand as below is enough to trigger the dispatch_protocol_error message. No authentication required.

  /opt/thinlinc/lib/tlclient/ssh user@host
Comment 4 Henrik Andersson cendio 2018-05-17 07:02:08 CEST 
Debug log on sshd server:

May 17 06:26:46 hean01-desktop sshd[13224]: debug1: KEX done [preauth]
May 17 06:26:46 hean01-desktop sshd[13224]: dispatch_protocol_error: type 50 seq 3 [preauth]
May 17 06:26:46 hean01-desktop sshd[13224]: debug1: userauth-request for user test service ssh-connection method none [preauth]

From sshd.c

 /* authenticate user and start session */
 do_ssh2_kex();
 do_authentication2(authctxt);

do_authentication2() in auth2.c expects next message to be SSH2_MSG_SERVICE_REQUEST but receives a
SSH2_MSG_USERAUTH_REQUEST (50) as being logged as dispatch_protocol_error. After the wrong SSH2_MSG_USERAUTH_REQUEST a SSH2_MSG_USERAUTH_REQUEST is receive and everything goes along as expected.
Comment 8 Samuel Mannehed cendio 2018-05-21 11:08:31 CEST 
I verified that I could reproduce the problem using 4.9.0 client on both Fedora 28 and Windows 10 connecting to a Ubuntu 16.04 server. I saw the error once for the master connection and once for the agent connection in /var/auth.log.

I then verified that the problem was fixed using build 5788 of the client on both Fedora 28 and Windows 10.
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