** Description changed: [ Impact ] - Non-ascii visible chars are not properly rendered by clients, showing - their octal visualization. + Non-ascii visible chars (including back-slashes, new lines and so) are + not properly rendered by clients, showing their octal visualization. Such as: - Hello SSHD! We love \360\237\215\225! + Hello SSHD \\ We love \360\237\215\225! + + Instead of: + + Hello SSHD \ We love 🍕! + + This is particularly an issue when a server has configured keyboard + interactive authentication and a PAM module wants to show non-ASCII + characters such as a QR code for web authentication: + + When using an ubuntu server running authd for web authentication we may + end up having the login qrcode rendered such as + + \210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210 + https://ubuntu.com + 1337 + + Which is clearly unreadable. [ Test case ] ## Server preparation Enable PAM and keyboard interactive authentication in a ssh server: Add a configuration file such as: /etc/ssh/sshd_config.d/test-ssh-pam.conf Containing: UsePAM yes KbdInteractiveAuthentication yes + # This was working already; here to check potential regressions + ForceCommand bash -c "echo Hello from SSHD \ We also love 🍕!; $SHELL" + + It's also suggested to check for regressions using a `Banner` option in + sshd, pointing to a file with utf-8 contents. Restart the server: sudo systemctl restart ssh.service Edit the sshd PAM configuration file, adding as first line: - auth requisite pam_echo.so Hello SSHD! We love 🍕! + auth requisite pam_echo.so Hello SSHD \ We love 🍕! Can be done with the command: - sudo sed '1 i\auth requisite pam_echo.so Hello SSHD! We love 🍕!' -i /etc/pam.d/sshd + sudo sed '1 iauth requisite pam_echo.so Hello SSHD! \\ We love 🍕!' \ + -i /etc/pam.d/sshd ## Client test In the same host: ssh -o PubkeyAuthentication=no \ -o PasswordAuthentication=no \ -o PreferredAuthentications=keyboard-interactive \ $USER@localhost The client should show: - Hello SSHD-dev in devel schroot! Want some 🍕? + Hello SSHD \ We love 🍕! ($USER@localhost) Password: + ... + Hello from SSHD \ We also love 🍕! Retry the same with another host and without keyboard authentication enabled in the server side. ## Cleanup Revert the changes done in the cleanup phase, after test is done sudo sed '/pam_echo\.so/d' -i /etc/pam.d/sshd sudo rm /etc/ssh/sshd_config.d/test-ssh-pam.conf [ Regression potential ] - SSH info messages are not shown by the client. + SSH info messages are not shown by the client. Even though those aren't + covered by this change, it's important to check for regressions in any + output that SSH exposes to the user. So banners and other messages + should be checked for regressions. - These kind of messages are normally shown only when PAM is enabled in - the server side, so it should not affect the normal behavior. + These kind of messages are normally shown only when PAM *and* keyboard + interaction are enabled in the server side, so it should not affect the + default ubuntu servers behavior.
** Description changed: [ Impact ] Non-ascii visible chars (including back-slashes, new lines and so) are not properly rendered by clients, showing their octal visualization. Such as: - Hello SSHD \\ We love \360\237\215\225! + Hello SSHD \\ We love \360\237\215\225! Instead of: - Hello SSHD \ We love 🍕! + Hello SSHD \ We love 🍕! This is particularly an issue when a server has configured keyboard interactive authentication and a PAM module wants to show non-ASCII characters such as a QR code for web authentication: When using an ubuntu server running authd for web authentication we may end up having the login qrcode rendered such as \210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210\342\226\210 - https://ubuntu.com - 1337 + https://ubuntu.com + 1337 Which is clearly unreadable. [ Test case ] ## Server preparation Enable PAM and keyboard interactive authentication in a ssh server: Add a configuration file such as: /etc/ssh/sshd_config.d/test-ssh-pam.conf Containing: UsePAM yes KbdInteractiveAuthentication yes # This was working already; here to check potential regressions ForceCommand bash -c "echo Hello from SSHD \ We also love 🍕!; $SHELL" It's also suggested to check for regressions using a `Banner` option in sshd, pointing to a file with utf-8 contents. Restart the server: sudo systemctl restart ssh.service Edit the sshd PAM configuration file, adding as first line: auth requisite pam_echo.so Hello SSHD \ We love 🍕! Can be done with the command: sudo sed '1 iauth requisite pam_echo.so Hello SSHD! \\ We love 🍕!' \ - -i /etc/pam.d/sshd + -i /etc/pam.d/sshd ## Client test In the same host: ssh -o PubkeyAuthentication=no \ -o PasswordAuthentication=no \ -o PreferredAuthentications=keyboard-interactive \ $USER@localhost The client should show: Hello SSHD \ We love 🍕! ($USER@localhost) Password: ... Hello from SSHD \ We also love 🍕! Retry the same with another host and without keyboard authentication enabled in the server side. + To verify the fix in more complex scenario it's possible to follow the instructions of configuring authd: + - https://github.com/ubuntu/authd/wiki/05--How%E2%80%90to-log-in-over-SSH + + Once authd is configured, the user should be able to scan a QrCode from + a ssh session. + ## Cleanup Revert the changes done in the cleanup phase, after test is done sudo sed '/pam_echo\.so/d' -i /etc/pam.d/sshd sudo rm /etc/ssh/sshd_config.d/test-ssh-pam.conf [ Regression potential ] SSH info messages are not shown by the client. Even though those aren't covered by this change, it's important to check for regressions in any output that SSH exposes to the user. So banners and other messages should be checked for regressions. These kind of messages are normally shown only when PAM *and* keyboard interaction are enabled in the server side, so it should not affect the default ubuntu servers behavior. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2077576 Title: SSH client doesn't handle properly non-ASCII chars To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/openssh/+bug/2077576/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
