I used the process described in bug 1557 today to attempt to capture debug information. I didn't get anything useful, and no clues as to why the X2Go client is crashing with strong ciphers.

x2go-INFO-1> "Starting X2Go Client 4.1.2.3..."
x2go-WARNING-1> English language requested, not loading translator.
x2go-WARNING-1> English language requested, not loading translator.
x2go-DEBUG-../src/onmainwindow.cpp:10902> Getting X.Org Server settings.
x2go-INFO-3> "Started X2Go Client."
x2go-DEBUG-../src/onmainwindow.cpp:626> "$HOME=C:/Users/Adam"
x2go-DEBUG-../src/onmainwindow.cpp:2359> Reading 1 sessions from config file.
x2go-DEBUG-../src/onmainwindow.cpp:13415> libssh not initialized yet. Initializing.
x2go-DEBUG-../src/pulsemanager.cpp:369> pulseaudio --version returned:"pulseaudio 13.0

"

x2go-DEBUG-../src/onmainwindow.cpp:10805> Starting helper servers for Windows ...
x2go-DEBUG-../src/onmainwindow.cpp:10972> "/cygdrive/C/Users/Adam/.x2go/var" cygwin var path
x2go-DEBUG-../src/onmainwindow.cpp:11060> "C:/Users/Adam/.x2go/etc/sshd_config created."
x2go-DEBUG-../src/onmainwindow.cpp:10467> Resolved localhost.
x2go-DEBUG-../src/onmainwindow.cpp:2853> Creating QPixmap with session icon: '":/img/icons/128x128/x2gosession.png"'.
x2go-DEBUG-../src/pulsemanager.cpp:227> pulse started with arguments ("--exit-idle-time=-1", "-n", "-F",
"C:\Users\Adam\.x2go\pulse\config.pa", "-p", "C:\Program Files (x86)\x2goclient\pulse\lib\pulse-13.0\modules",
"--log-level=debug", "--verbose", "--log-target=file:C:\Users\Adam\.x2go\pulse\pulse.log") - waiting for it to
finish...
x2go-DEBUG-../src/onmainwindow.cpp:10489> Port is free: 7022
x2go-DEBUG-../src/onmainwindow.cpp:11411> Logging cygwin sshd to: "C:/Users/Adam/.x2go/sshLogs/p12616.log"
x2go-DEBUG-../src/onmainwindow.cpp:11425> Creating desktop: x2go_Adam
x2go-DEBUG-../src/onmainwindow.cpp:10467> Resolved localhost.
x2go-DEBUG-../src/onmainwindow.cpp:10495> Port already in use: 7022
x2go-DEBUG-../src/onmainwindow.cpp:10467> Resolved localhost.
x2go-DEBUG-../src/onmainwindow.cpp:10495> Port already in use: 7022
x2go-DEBUG-../src/onmainwindow.cpp:11522> User mode OpenSSH server started successfully.
x2go-INFO-8> "Starting connection to server: localhost:49199"
x2go-DEBUG-../src/onmainwindow.cpp:2954> Starting new ssh connection to server:"localhost":"49199" krbLogin: false
x2go-DEBUG-../src/sshmasterconnection.cpp:168> SshMasterConnection, host "localhost"; port 49199; user "Adam.Dorsey";
useproxy false; proxyserver ""; proxyport 22
x2go-DEBUG-../src/sshmasterconnection.cpp:248> Starting SSH connection without Kerberos authentication.
x2go-DEBUG-../src/sshmasterconnection.cpp:250> SshMasterConnection, instance SshMasterConnection(0x548e2a8) created.
x2go-DEBUG-../src/sshmasterconnection.cpp:492> SshMasterConnection, instance SshMasterConnection(0x548e2a8) entering
thread.
x2go-DEBUG-../src/sshmasterconnection.cpp:573> Setting SSH directory to C:/Users/Adam/ssh
x2go-DEBUG-../src/sshmasterconnection.cpp:795> Session port before config file parse: 49199
x2go-DEBUG-../src/sshmasterconnection.cpp:805> Session port after config file parse: 49199

On Tue, Aug 17, 2021 at 11:45 AM Adam Dorsey - NOAA Affiliate <adam.dorsey@noaa.gov> wrote:

A quick update for this bug:

Today I tested the same scenario (Cipher aes128-ctr) on our test cluster using the latest Windows snapshot client, version 4.1.2.3-2021.07.13-df4a8ec. The issue as described in this bug report is still present.

Thanks,
Adam

On Fri, Mar 19, 2021 at 2:28 PM Adam Dorsey - NOAA Affiliate <adam.dorsey@noaa.gov> wrote:
I can confirm this issue in my own environment as well. X2Go server version is 4.1.0.3-9.el7 running on CentOS 7. Affected users are running X2Go client version 4.1.2.2 on Windows 10 (though this may affect other Windows versions as well).

We forced the use of the aes128-ctr cipher yesterday on our cluster login nodes to resolve a security issue raised by our security team. To do this, we added the following line to our SSH server config file:

Ciphers aes128-ctr

After making this change, several users running the X2Go client on Windows 10 could no longer connect. We found this bug report, and subsequently reverted the above change, which resolved the issue.

Please note that Linux clients appeared to be unaffected by this issue; I was able to connect from a workstation running X2Go client version 4.1.2.2 on Ubuntu Linux 20.04 without any issues.

--
Adam Dorsey
NOAA RDHPCS Systems Administrator Site Lead
CSRA / RedLine Performance Solutions, LLC

NOAA NESCC
1000 Galliher Drive, Suite 333, Fairmont, WV 26554
office: (304) 367-2882
cell: (304) 685-9345
adam.dorsey@noaa.gov

--
Adam Dorsey
NOAA RDHPCS Systems Administrator Site Lead
CSRA / RedLine Performance Solutions, LLC

NOAA NESCC
1000 Galliher Drive, Suite 333, Fairmont, WV 26554
office: (304) 367-2882
cell: (304) 685-9345
adam.dorsey@noaa.gov
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